Mexico City, Dec 29 (IANS): As the White House mulls whether or not to seal off the US' southern border, Mexican President Andres Manuel Lopez Obrador has said the decision is Washington's "domestic issue".

"We have not issued an opinion on the matter because it is a domestic issue for the US government and we prefer to abstain from commenting," Xinhua news agency quoted Obrador as saying at a press conference on Friday.

"We are always looking to maintain very good ties with the US," he added.

US President Donald Trump has raised the prospect of completely sealing off the border unless Democratic-controlled Congress agrees to fund his controversial border wall.

"We build a Wall or... close the Southern Border," Trump had tweeted.

To pressure lawmakers, Trump on December 22 sparked a partial shutdown of the federal government.

He wants $5 billion for the wall, which was a central promise of his 2016 presidential campaign.

Democrats have agreed to approve $1.3 billion to bolster security at the border but have long opposed the building of a wall.