Mexico has invited experts from the U.S. National Transportation Safety Board to investigate a helicopter crash that killed the governor of the western state of Puebla and her husband.

Mexico's assistant transportation secretary says the invitation was made 'to leave no doubts' about the Monday crash that killed opposition Gov. Martha Erika Alonso and her husband, ex-Gov. Rafael Moreno Valle.

Carlos Moran said Tuesday that the manufacturers of the helicopter and its engines will participate in the investigation, and it was too early to determine whether mechanical problems played a role.

Scroll down for video

Mexican governor Martha Erika Alonso (right) was killed in a helicopter crash Monday alongside her spouse Rafael Moreno Valle Rosas (left)

Mexico's assistant transportation secretary says the invite to the U.S. National Trasportation Safety Board was made 'to leave no doubts' about the crash

Two pilots and a third passenger also died in the crash. The pilots were described as experienced, though one had spent much of his career flying fixed-wing aircraft.

Alsonso, 45, had only been sworn into office ten days ago after independent electoral authorities dismissed the challenge.

Meanwhile her husband Valle was also the former Puebla governor and a prominent figure in the opposition National Action Party who had vied unsuccessfully for the party's presidential nomination and its internal leadership. The couple did not appear to have children.

The aircraft went down in Huetjotzingo, a small city near the second largest in Mexico, Puebla

Mexico is still reeling from the loss and on Monday afternoon, President Andres Manuel Lopez Obrador paid tribute to the couple, while Marko Cortes, head of the National Action Party, tweeted he was deeply saddened.

'We are in mourning,' he wrote.

The Agusta 109 helicopter suffered an 'apparent failure which hasn't been determined yet' shortly after taking off from Puebla airport bound for Mexico City on Monday.

Alsonso, 45, had only been sworn into office ten days ago after independent electoral authorities dismissed the challenge

The couple did not appear to have children

It crashed in the municipality of Santa Maria Coronango, which is about 3.5 miles north of the city's main airport on the western outskirts, federal Public Security Secretary Alfonso Durazo told a news conference.

Images of the crash showed a shattered, still smoldering aircraft on the edge of a scorched patch of cornfield.

The helicopter pilot and co-pilot have been identified as Captain Roberto Cope Obregon and Captain Marco Antonio Cabera Romero, according to Public Security and Civil Protection Secretary Alfonso Durazo.

The other passenger has not yet been named.

Plumes of smoke could be seen as the helicopter was still on fire when others arrived at the scene

A forensic member was pictured on the scene after the crash on Monday

A helicopter was pictured over the site on Monday following the incident

Mexican Civil Aviation authorities are investigating the cause.

Both federal and state officials said they had opened investigations into the cause - a potentially sensitive case because President Andres Manuel Lopez Obrador's Morena party had challenged the validity of Alonso's election in July.

She was sworn in 10 days ago after independent electoral authorities dismissed the challenge.

State spokesman Maximiliano Cortazar demanded a 'transparent, impartial and independent' investigation.

The Mexican president tweeted his condolences on Monday, confirming their death

Alonso was the first female governor of Puebla and only the seventh nationwide

Rafael Moreno Valle Rosas became Senator in September and was governor from 2011 to 2017. In 2015 his wife was the First Lady of Puebla and the second highest ranking in her PAN party

Lopez Obrador expressed his 'deepest condolences' via Twitter to the family of on Monday evening.

Moreno Valle governed the central state from 2011 to 2017 and was currently a federal senator. Opponents alleged that he had manipulated the election to hand power to his wife.

Government agencies and scores of officials, including former President Enrique Pena Nieto, also expressed condolences via statements and social media.

Foreign Minister Marcelo Ebrard tweeted: 'I said hello to [Moreno] in the Senate just a few days ago. Those of us who had the opportunity to know them are sad and troubled.'

Conservative Alonso became the first female governor of Puebla less than two weeks ago on December 14.

The center-right candidate narrowly beat opposition from President Obrador's favored Miguel Barbosa Huerta on July 1.

Teams from the State Attorney's Office, Attorney General's Office and state Civil Protect personnel were on the scene

Security members work at the helicopter crash site in Coronango, Puebla, Mexico

The cause of the accident was still unknown on Monday night

Emergency rescue personnel, the army and the police arrived to the scene of the crash

A helicopter of Puebla's government flew over the scene of the incident as it turned late

Her election triggered a violent and hotly-contested reaction and on December 9 a Federal Electoral Tribunal had to validate the results due to accusations of fraud form her National Regeneration Movement (also known as the Morena party) opponent Luis Miguel Barbosa.

Leftist Barbosa said in an interview with Milenio, that it's a tragedy and 'it is up to the authorities to do the same so that the causes of the accident are perfectly clear,' Animal Politico reported.

The reported he declined to answer what would happen now the pair are gone.

'It is not the time to make political comments, it is time for solidarity, beyond the political rivalry that I had with both,' he reportedly said. 'I do not want to give an opinion on the succession, it's time to be supportive.'

The couple celebrated their 14th anniversary this year and shared a dog

Once Congress appoints an interim governor, an election - lasting between three and five months - must be announced within 10 days.

Federal electoral institute official Benito Nacif confirmed it would happen.

The fact the accident occurred just days after Alonso - who celebrated her birthday only one week ago - took office triggered speculation of foul play on social media, Reuters reported.

A number of Mexican politicians have died in aircraft accidents in the past few years, including federal interior ministers in 2008 and 2011.

Both were members of the PAN.

BBC News reported that 13 people died earlier this year when a minister's helicopter crashed into a crowd. The minister survived.

From 2015, Puebla First Lady Alonso became second in the power structure of the party behind her husband.

Moreno became a federal senator in September. He shared the same name as his father who was Governor of Puebla from 1969 to 1972.

The couple married in 2004, celebrated their 14th anniversary this January and shared a dog.