April 26 (Reuters) - President Donald Trump tweeted support for a U.S. bid to co-host the 2026 soccer World Cup with a veiled threat against nations that might oppose it, prompting soccer's governing body to refer to guidelines that warn against political influence over bids.

Morocco is the only rival to a joint bid to stage the event from the United States, Canada and Mexico, with the FIFA Congress due to choose the hosts in Moscow on June 13.

"The U.S. has put together a STRONG bid w/ Canada & Mexico for the 2026 World Cup," Trump tweeted.

"It would be a shame if countries that we always support were to lobby against the U.S. bid. Why should we be supporting these countries when they don’t support us (including at the United Nations)?"

The U.S. has put together a STRONG bid w/ Canada & Mexico for the 2026 World Cup. It would be a shame if countries that we always support were to lobby against the U.S. bid. Why should we be supporting these countries when they don’t support us (including at the United Nations)? — Donald J. Trump (@realDonaldTrump) April 26, 2018

Soccer's governing body FIFA has faced repeated ethics questions over past bids to host the tournament.

In a statement to Reuters, FIFA said: "As a general rule, we cannot comment on specific statements in connection with the bidding process. We can only refer to the FIFA Regulations for the selection of the venue for the final competition of the 2026 FIFA World Cup, and in particular to the Bid Rules of Conduct incorporated therein."

The Bid Rules of Conduct contain an explicit warning against activities by bidding country governments which "may adversely affect the integrity of the Bidding Process and create an undue influence on the Bidding Process."

See inside this year's World Cup draw:

12 PHOTOS Inside the 2018 World Cup draw See Gallery Inside the 2018 World Cup draw MOSCOW, RUSSIA - DECEMBER 1, 2017: Draw assistant, Russian Football Union Vice President Nikita Simonyan holds a slip reading Russia at the Final Draw for the 2018 FIFA World Cup at the State Kremlin Palace. Stanislav Krasilnikov/TASS (Photo by Stanislav Krasilnikov\TASS via Getty Images) A boy plays with the official ball Telstar 18 at the end of the 2018 FIFA World Cup football tournament final draw at the State Kremlin Palace in Moscow on December 1, 2017. The 2018 FIFA World Cup will be held between June 14 and July 15, 2018 in 11 Russian cities. / AFP PHOTO / Kirill KUDRYAVTSEV (Photo credit should read KIRILL KUDRYAVTSEV/AFP/Getty Images) MOSCOW, RUSSIA DECEMBER 1, 2017: FIFA President Gianni Infantino (L) and Russia's President Vladimir Putin attend the Final Draw for 2018 FIFA World Cup at the State Kremlin Palace. Alexei Nikolsky/Russian Presidential Press and Information Office/TASS (Photo by Alexei Nikolsky\TASS via Getty Images) MOSCOW, RUSSIA - DECEMBER 01: Russian President Vladimir Putin (left), former Russian football player Nikita Simonyan (center) and Brazil football player Pele (right) before the draw ceremony on December 1, 2017 in Moscow, Russia. (Photo by Dmitry Azarov/Kommersant via Getty Images) MOSCOW, RUSSIA - DECEMBER 1, 2017: Retired Brazilian football star Pele ahead of the 2018 FIFA World Cup final draw at the State Kremlin Palace. Alexei Nikolsky/Russian Presidential Press and Information Office/TASS (Photo by Alexei Nikolsky\TASS via Getty Images) National team coaches pose on stage after the Final Draw for the 2018 FIFA World Cup football tournament at the State Kremlin Palace in Moscow on December 1, 2017. The 2018 FIFA World Cup will be held from June 14 and July 15, 2018, in 11 Russian cities. / AFP PHOTO / Mladen ANTONOV (Photo credit should read MLADEN ANTONOV/AFP/Getty Images) A picture shows the pots ahead of the 2018 FIFA World Cup football tournament final draw at the State Kremlin Palace in Moscow on December 1, 2017. The 2018 FIFA World Cup will be held between June 14 and July 15, 2018 in 11 Russian cities. / AFP PHOTO / Yuri KADOBNOV (Photo credit should read YURI KADOBNOV/AFP/Getty Images) MOSCOW, RUSSIA - DECEMBER 01: The final draw of FIFA World Cup Russia 2018 in the Concert Hall of Kremlin Palace on December 1, 2017 in Moscow, Russia. (Photo by Dmitry Lebedev/Kommersant via Getty Images) Russian President Vladimir Putin (L) toasts with football legends, draw assistants and other attendees ahead of the Final Draw for the 2018 FIFA World Cup football tournament at the State Kremlin Palace in Moscow on December 01, 2017. / AFP PHOTO / SPUTNIK / Alexey NIKOLSKY (Photo credit should read ALEXEY NIKOLSKY/AFP/Getty Images) MOSCOW, RUSSIA - DECEMBER 01: A general view during the Final Draw for the 2018 FIFA World Cup Russia at the State Kremlin Palace on December 1, 2017 in Moscow, Russia. (Photo by Shaun Botterill/Getty Images) Russian singer Alsou performs during the 2018 FIFA World Cup football tournament final draw at the State Kremlin Palace in Moscow on December 1, 2017. The 2018 FIFA World Cup will be held between June 14 and July 15, 2018 in 11 Russian cities. / AFP PHOTO / Kirill KUDRYAVTSEV (Photo credit should read KIRILL KUDRYAVTSEV/AFP/Getty Images) MOSCOW, RUSSIA - DECEMBER 01: The World Cup trophy is seen during the Final Draw for the 2018 FIFA World Cup Russia at the State Kremlin Palace on December 1, 2017 in Moscow, Russia. (Photo by Michael Regan - FIFA/FIFA via Getty Images) Up Next See Gallery Discover More Like This HIDE CAPTION SHOW CAPTION of SEE ALL BACK TO SLIDE

Mexico's president Enrique Pena Nieto responded positively to Trump on twitter.

"We can have differences but football unites us. Together we support the candidacy of Mexico, Canada and USA as the headquarters of the World Cup 2026," he wrote.

The North American bid committee said it was pleased to have Trump's support.

"From the beginning, we have received strong support from the Canadian, Mexican, and United States governments. We are grateful for that support and together our three countries are ready to welcome players and fans from around the world to an extraordinary FIFA World Cup in 2026."

The North American bid boasts large stadiums and excellent infrastructure but is no certainty to win the June vote.

Related: See inside Trump's first state dinner:

41 PHOTOS Inside President Trump's first State Dinner See Gallery Inside President Trump's first State Dinner United States President Donald Trump and first lady Melania Trump welcome French President Emmanuel Macron and his wife Brigitte for a State Dinner at the White House in Washington, U.S., April 24, 2018. REUTERS/Brian Snyder White House Advisor Jared Kushner and wife Ivanka Trump arrive in the Booksellers Area of the White House to attend a state dinner honoring France's President Emmanuel Macron on April 24, 2018 in Washington, DC. (Photo by MANDEL NGAN / AFP) (Photo credit should read MANDEL NGAN/AFP/Getty Images) US Treasury Secretary Steven Mnuchin and wife Louise Linton arrive in the Booksellers Area of the White House to attend a state dinner honoring France's President Emmanuel Macron on April 24, 2018 in Washington, DC. (Photo by MANDEL NGAN / AFP) (Photo credit should read MANDEL NGAN/AFP/Getty Images) Tables for the State Dinner for French President Emmanuel Macron are shown in the State Dining Room of the White House in Washington, U.S., April 23, 2018. REUTERS/Joshua Roberts Paul Ryan and his wife arrive in the Booksellers Area of the White House to attend a state dinner honoring France's President Emmanuel Macron on April 24, 2018 in Washington, DC. (Photo by MANDEL NGAN / AFP) (Photo credit should read MANDEL NGAN/AFP/Getty Images) US Vice President Mike Pence and wife Karen arrive in the Booksellers Area of the White House to attend a state dinner honoring France's President Emmanuel Macron on April 24, 2018 in Washington, DC. (Photo by MANDEL NGAN / AFP) (Photo credit should read MANDEL NGAN/AFP/Getty Images) Stephen A. Schwarzman, chairman and CEO of The Blackstone Group, arrives in the Booksellers Area of the White House to attend a state dinner honoring France's President Emmanuel Macron on April 24, 2018 in Washington, DC. (Photo by MANDEL NGAN / AFP) (Photo credit should read MANDEL NGAN/AFP/Getty Images) White House Press Secretary Sarah Huckabee Sanders and husband Bryan Sanders arrive in the Booksellers Area of the White House to attend a state dinner honoring French President Emmanuel Macron on April 24, 2018 in Washington, DC. (Photo by MANDEL NGAN / AFP) (Photo credit should read MANDEL NGAN/AFP/Getty Images) A place setting for the State Dinner for French President Emmanuel Macron is shown in the State Dining Room of the White House in Washington, U.S., April 23, 2018. REUTERS/Joshua Roberts CEO of Apple Tim Cook arrives with Lisa Jackson in the Booksellers Area of the White House to attend a state dinner honoring France's President Emmanuel Macron on April 24, 2018 in Washington, DC. (Photo by MANDEL NGAN / AFP) (Photo credit should read MANDEL NGAN/AFP/Getty Images) United States President Donald Trump and first lady Melania Trump welcome French President Emmanuel Macron and his wife Brigitte for a State Dinner at the White House in Washington, U.S., April 24, 2018. REUTERS/Brian Snyder US Senator John Kennedy (R-LA) arrives in the Booksellers Area of the White House to attend a state dinner honoring France's President Emmanuel Macron on April 24, 2018 in Washington, DC. (Photo by MANDEL NGAN / AFP) (Photo credit should read MANDEL NGAN/AFP/Getty Images) White House Advisor Stephen Miller arrives in the Booksellers Area of the White House to attend a state dinner honoring French President Emmanuel Macron on April 24, 2018 in Washington, DC. (Photo by MANDEL NGAN / AFP) (Photo credit should read MANDEL NGAN/AFP/Getty Images) Tables for the State Dinner for French President Emmanuel Macron are shown in the State Dining Room of the White House in Washington, U.S., April 23, 2018. REUTERS/Joshua Roberts US policy strategist Dina Powell and husband Richard Powell arrive in the Booksellers Area of the White House to attend a state dinner honoring France's President Emmanuel Macron on April 24, 2018 in Washington, DC. (Photo by MANDEL NGAN / AFP) (Photo credit should read MANDEL NGAN/AFP/Getty Images) Media mogul Rupert Murdoch and wife Jerry Hall arrive in the Booksellers Area of the White House to attend a state dinner honoring France's President Emmanuel Macron on April 24, 2018 in Washington, DC. (Photo by MANDEL NGAN / AFP) (Photo credit should read MANDEL NGAN/AFP/Getty Images) Marillyn A. Hewson, CEO of Lockheed Martin, arrives in the Booksellers Area of the White House to attend a state dinner honoring French President Emmanuel Macron on April 24, 2018 in Washington, DC. (Photo by MANDEL NGAN / AFP) (Photo credit should read MANDEL NGAN/AFP/Getty Images) Tables for the State Dinner for French President Emmanuel Macron are shown from the Cross Hall of the White House in Washington, U.S., April 23, 2018. REUTERS/Joshua Roberts United States President Donald Trump and first lady Melania Trump welcome French President Emmanuel Macron and his wife Brigitte for a State Dinner at the White House in Washington, U.S., April 24, 2018. REUTERS/Brian Snyder Chief Justice John Roberts and his wife arrive in the Booksellers Area of the White House to attend a state dinner honoring France's President Emmanuel Macron on April 24, 2018 in Washington, DC. (Photo by MANDEL NGAN / AFP) (Photo credit should read MANDEL NGAN/AFP/Getty Images) Cherry blossom flowers decorate the Cross Hall for the State Dinner for France's President Emmanuel Macron at the White House in Washington, U.S., April 23, 2018. REUTERS/Joshua Roberts Ivanka Trump and husband Jared Kushner, Trump's senior advisor arrive in the Booksellers Area of the White House to attend a state dinner honoring French President Emmanuel Macron on April 24, 2018 in Washington, DC. (Photo by MANDEL NGAN / AFP) (Photo credit should read MANDEL NGAN/AFP/Getty Images) Former US secretary of state Henry Kissinger arrives in the Booksellers Area of the White House to attend a state dinner honoring France's President Emmanuel Macron on April 24, 2018 in Washington, DC. (Photo by MANDEL NGAN / AFP) (Photo credit should read MANDEL NGAN/AFP/Getty Images) A menu for the State Dinner for French President Emmanuel Macron is shown in the State Dining Room of the White House in Washington, U.S., April 23, 2018. REUTERS/Joshua Roberts United States President Donald Trump and first lady Melania Trump welcome French President Emmanuel Macron and his wife Brigitte for a State Dinner at the White House in Washington, U.S., April 24, 2018. REUTERS/Carlos Barria US Secretary of Defense James Mattis arrive in the Booksellers Area of the White House to attend a state dinner honoring French President Emmanuel Macron on April 24, 2018 in Washington, DC. (Photo by MANDEL NGAN / AFP) (Photo credit should read MANDEL NGAN/AFP/Getty Images) Tables for the State Dinner for French President Emmanuel Macron are shown in the State Dining Room of the White House in Washington, U.S., April 23, 2018. REUTERS/Joshua Roberts WASHINGTON, DC - APRIL 24: U.S President Donald Trump, and U.S. first lady Melania welcome French President Emmanuel Macron, French first lady Brigitte Macron after their arrival at the North Portico for before a State Dinner at the White House April 24, 2018 in Washington, DC. Trump is hosting Macron for a two-day official visit that included dinner at George Washington's Mount Vernon, a tree planting on the White House South Lawn and a joint news conference. (Photo by Mark Wilson/Getty Images) Former US secretary of state Henry Kissinger and his wife Nancy Kissinger arrive in the Booksellers Area of the White House to attend a state dinner honoring France's President Emmanuel Macron on April 24, 2018 in Washington, DC. (Photo by MANDEL NGAN / AFP) (Photo credit should read MANDEL NGAN/AFP/Getty Images) US President Donald Trump and First Lady Melania Trump welcome French President Emmanuel Macron and his wife, Brigitte Macron, as they arrive for a State Dinner at the North Portico of the White House in Washington, DC, April 24, 2018. (Photo by SAUL LOEB / AFP) (Photo credit should read SAUL LOEB/AFP/Getty Images) United States Secretary of the Treasury Steven Mnuchin and his wife Louise Linton arrive in the Booksellers Area of the White House to attend a state dinner honoring France's President Emmanuel Macron on April 24, 2018 in Washington, DC. (Photo by MANDEL NGAN / AFP) (Photo credit should read MANDEL NGAN/AFP/Getty Images) French Foreign Minister Jean-Yves Le Drian arrives in the Booksellers Area of the White House to attend a state dinner honoring France's President Emmanuel Macron on April 24, 2018 in Washington, DC. (Photo by MANDEL NGAN / AFP) (Photo credit should read MANDEL NGAN/AFP/Getty Images) Cherry blossom flowers decorate the Cross Hall for the State Dinner for France's President Emmanuel Macron at the White House in Washington, U.S., April 23, 2018. REUTERS/Joshua Roberts Henry R. Kravis arrives in the Booksellers Area of the White House to attend a state dinner honoring France's President Emmanuel Macron on April 24, 2018 in Washington, DC. (Photo by MANDEL NGAN / AFP) (Photo credit should read MANDEL NGAN/AFP/Getty Images) David Rubenstein, co-founder and co-executive chairman of The Carlyle Group, arrives in the Booksellers Area of the White House to attend a state dinner honoring French President Emmanuel Macron on April 24, 2018 in Washington, DC. (Photo by MANDEL NGAN / AFP) (Photo credit should read MANDEL NGAN/AFP/Getty Images) Chief of Staff John Kelly arrives in the Booksellers Area of the White House to attend a state dinner honoring France's President Emmanuel Macron on April 24, 2018 in Washington, DC. (Photo by MANDEL NGAN / AFP) (Photo credit should read MANDEL NGAN/AFP/Getty Images) Rupert Murdoch and Jerry Murdoch arrive in the Booksellers Area of the White House to attend a state dinner honoring France's President Emmanuel Macron on April 24, 2018 in Washington, DC. (Photo by MANDEL NGAN / AFP) (Photo credit should read MANDEL NGAN/AFP/Getty Images) US Defense Secretary James Mattis arrives in the Booksellers Area of the White House to attend a state dinner honoring French President Emmanuel Macron on April 24, 2018 in Washington, DC. (Photo by MANDEL NGAN / AFP) (Photo credit should read MANDEL NGAN/AFP/Getty Images) US President Donald Trump's pick for secretary of state, Mike Pompeo arrives in the Booksellers Area of the White House to attend a state dinner honoring France's President Emmanuel Macron on April 24, 2018 in Washington, DC. (Photo by MANDEL NGAN / AFP) (Photo credit should read MANDEL NGAN/AFP/Getty Images) US Rep. Kevin McCarthy (R-CA) arrives in the Booksellers Area of the White House to attend a state dinner honoring French President Emmanuel Macron on April 24, 2018 in Washington, DC. (Photo by MANDEL NGAN / AFP) (Photo credit should read MANDEL NGAN/AFP/Getty Images) Secretary of Commerce Wilbur Ross arrives in the Booksellers Area of the White House to attend a state dinner honoring France's President Emmanuel Macron on April 24, 2018 in Washington, DC. (Photo by MANDEL NGAN / AFP) (Photo credit should read MANDEL NGAN/AFP/Getty Images) Up Next See Gallery Discover More Like This HIDE CAPTION SHOW CAPTION of SEE ALL BACK TO SLIDE

The Moroccan bid team declined to comment on Trump's tweet.

The North American bid boasts large stadiums and excellent infrastructure but is no certainty to win the June vote.

The Morocco bid is expected to receive strong backing from FIFA's African and Middle East countries.

France plans to back Morocco, the country's football federation president told local media recently, while Russia, which will host the 2018 tournament from June 14-July 15, has said it will also vote for the north African nation's bid.

The United States previously hosted the World Cup in 1994.

FIFA member countries receive one vote each, no matter their size. (Reporting by Andrew Both in Cary, North Carolina; Editing by Ian Ransom and Peter Graff)

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