MEXICO CITY:The Mexican president's hesitation over congratulating Joe Biden on his U.S. presidential election win drew flack from several Latino Democratic lawmakers who warned it risked souring a restart to bilateral ties after years of tension under Donald Trump.

In an apparent bid to avoid friction with Trump, who has often used Mexico as a veritable political pinata, Mexican President Andres Manuel Lopez Obrador said on Saturday that he was going to wait until "all the legal matters have been resolved" before commenting on the results of the U.S. election.

Democratic Texas lawmaker Joaquin Castro, head of the House of Representatives Foreign Affairs Committee's oversight subcommittee, took to Twitter to categorize the move as "a stunning diplomatic failure."

Lopez Obrador's decision comes "at a time when the incoming Biden Administration is looking to usher in a new era of friendship and cooperation with Mexico," said Castro, who was a member of President Barack Obama's cabinet.

Castro was one of at least a half dozen Democratic lawmakers who criticised the Mexican president, including Arizona state senator Martin Quezada who said "this is beyond disappointing."

A Biden presidency is seen as a chance to reset ties that have frayed since Trump made his first White House bid, tarring Mexican migrants as rapists and gun-runners and vowing to keep them out with a border wall.

"I can't congratulate one candidate or the other. I want to wait until the electoral process is over," Lopez Obrador said at a Saturday press conference.

He has needed to walk a fine line with Trump, whose term is scheduled to end on Jan. 20. Under Trump's administration, Mexico has had to navigate abrupt demands to stem illegal migration or face trade tariffs.

Lopez Obrador came into office in late 2018 promising a more humane touch with the tens of thousands of migrants, mostly Central Americans fleeing from entrenched violence and poverty, that traverse Mexico to get to the U.S. southern border.

But after Trump threatened to upend $600 billion in annual bilateral trade with Mexico, Lopez Obrador used the newly created National Guard military police to help stem the flow of migrants and acquiesced to have migrants wait for their U.S. court dates on Mexican soil.

"AMLO has been a co-conspirator in Donald Trump's efforts to undermine the human rights of vulnerable asylum seekers," said Congresswoman Veronica Escobar, using an acronym for Lopez Obrador's name.

His reluctance to comment on the U.S. election results stands in contrast to congratulations offered to Bolivia's former President Evo Morales last year despite opposition claims of fraud in that re-election bid.

It also stands in contrast to the wave of congratulations for Biden from world leaders despite Trump's protests that the election is not over.

Trump has filed a raft of lawsuits to challenge the results, but electoral officials in states across the country say there has been no evidence of significant fraud, and legal experts say Trump's efforts are unlikely to succeed.

"President Lopez Obrador, American voters have spoken and Joe Biden is our President Elect. He won fair and square. Don't get left behind by the train," warned Mexican-born Congressman Jesus "Chuy" Garcia.