Washington, April 6

US President Barack Obama said on Tuesday that campaign trail rhetoric from leading presidential candidates was damaging the US in the eyes of foreign leaders.

He said he receives questions "constantly" from fellow officials about the "wackier suggestions that are being made" in the race to secure the Republican nomination, reports CNN.

He said those suggestions were not coming only from presidential front-runner Donald Trump, as he called some of Texas Senator Ted Cruz's immigration proposals "draconian".

"People expect the president of the United States and the elected officials in this country to treat these problems seriously," Obama said during an appearance in the White House briefing room in which he discussed the US economy, but was responding to a reporter's question on the state of the 2016 race.

"They don't expect half-baked notions coming out of the White House. We can't afford that," the president said.

Trump would 'cut off cash to Mexico' to pay for border wall

Republican presidential candidate Donald Trump has said he would cut off money sent to Mexico to force them to pay for a border wall with the US.

In a memo to the Washington Post, the businessman said he would threaten to change a law to cut off cash transfers.

The prospect of losing a vital source of income would force Mexico into a "one-time payment" of $5-10 billion, said Trump.

Voters in Wisconsin were picking their presidential candidates.

They were going to the polls in a vote that could reshape the Republican race, with front-runner Trump facing a strong challenge from Texas Senator Ted Cruz.

Asked about the memo at a campaign stop in Wisconsin, he said he stood by it.

"Absolutely, 100 percent," Trump told reporters. "The wall is a fraction of the kind of money in many ways that Mexico takes from the US."

Building a border wall with Mexico has been a core message of Trump's campaign but until now he has not said in much detail how he would make Mexico pay for it.

The Mexican central bank said that money sent home from overseas hit nearly $24.8 billion last year, more than its oil revenues.

The law Trump wishes to changes, as outlined in his memo, is part of the US Patriot Act - he would stop anyone living illegally in the US from sending money overseas.

Just the threat of enacting this would make Mexico "immediately protest," the Trump memo reads, and they would be compelled to pay for the wall.

He also proposed raising visa fees and cancelling visas for Mexicans.