San José (AFP) - Mexican President Enrique Pena Nieto said on Wednesday he is working on "a new relationship" with the US and thanked Latin American neighbors for support as Mexico faces "big challenges" with its vital trading partner.

His comments were made at a one-day summit in Costa Rica's capital San Jose that gathered leaders from Mexico, Central America and Colombia.

US President Donald Trump, who took office in late January, has vowed to renegotiate the North American Free Trade Agreement (NAFTA) between the United States, Mexico and Canada.

Trump has also stepped up anti-immigration policies affecting Latin Americans, and is moving forward with a commitment to build a wall along the US-Mexico border.

Pena Nieto thanked his counterparts for "the displays of solidarity and trust they have shown Mexico in these recent months as Mexico faces very big challenges in building a new relationship with the United States government."

The Mexican president did not go into details about the state of play between his country and the US.

But relations are at their lowest point in years.

- US-Mexico trade -

Mexico sends 80 percent of its exports to the United States, with which it has a $60 billion trade surplus.

Trump has asserted that NAFTA is costing US manufacturing jobs and he is promoting protectionist policies, including consideration of a border adjustment tax on imports.

Mexico is said to be weighing cuts in the $2.3 billion in corn it imports from the United States if NAFTA negotiations go sour.

Pena Nieto told the summit: "We are sure that we are going to be able to reach an understanding that will be positive for both our nations."

He said he would keep the countries represented at the summit informed of aspects of its talks with the US that would affect them.

Colombian President Juan Manuel Santos also expressed concern at Trump's announcement on Tuesday that the US would scrap rules designed to curb America's global-warming emissions. The United Nations has said Colombia is at high risk from climate change.

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"Here we have a new world more dangerous, of greater risk," he said.

- 'Ominous shift' -

The summit, begun in the Mexican town of Tuxtla 26 years ago, is a regular event taking place every couple of years. It is aimed at bolstering cooperation on regional infrastructure, energy, health and environmental issues.

But this year the main topic weaving through speeches and discussions was US policies under Trump.

Belize's foreign minister, Wilfred Elrington, highlighted a perceived "ominous shift" in North America and parts of Europe toward more protectionist stances.

In a closing joint statement, the leaders expressed "preoccupation over increased actions discriminating against migrant persons" and rejected the "criminalization of migrants."

Host President Luis Guillermo Solis of Costa Rica later told reporters those passages directly applied to Trump's plans for the border wall.

"Walls that exist between nations of the world should disappear because what they do is separate the human family," Solis said.

The closing statement also noted regional agreement on fighting drug trafficking and organized crime, and the need to respect measures to fight climate change.