Trump 'Absolutely Deadly Serious' About Tariffs Against Mexico – Chief of Staff

President Trump is "absolutely deadly serious" about imposing tariffs on Mexico unless the Mexican government does its part to help stop the flow of mostly Central American migrants pouring into the US, acting White House Chief of Staff Mick Mulvaney has said.

"He's absolutely deadly serious. In fact I fully expect these tariffs to go on to at least the 5 percent level on June 10. The president is deadly serious about fixing the situation at the southern border," Mulvaney said, speaking to Fox News Sunday host Chris Wallace.

"We've been talking about it for months. Six months ago we told everybody it was an emergency situation. Very few people believed us…the Democrats even refused to believe the facts six months ago. So it's real," Mulvaney added, referring to the migrant crisis.

Asked about what specifically Mexico would have to do to stem the flow, Mulvaney said there were "several" things, including securing their southern border with Guatemala. "That border's only a quarter as long as the border with the United States. They could secure that border."

"They could go after their domestic terrorist organisations, their criminal organisations, who are in the business of moving people across Mexico. Keep in mind that at any one time there are 100,000 migrants in Mexico making their way up to the United States. And lastly they could make Mexico a safe place for these people to claim asylum," Mulvaney said.

According to the official, the Trump administration "intentionally left the declaration [on possible tariffs] sort of ad hoc so that we can work with the Mexicans to make sure that things did get better."

Mulvaney also said he was confident US consumers would not be hit with the burden of paying for the tariffs on the estimated $350 billion in goods which the US imports from Mexico each year, saying the traditional economic thinking on this idea was wrong, and that the US already pays "hundreds of billions" of dollars to deal with the consequences of illegal immigration.

Earlier Sunday, President Trump fired off a series of tweets on the border security issue, accusing the Democrats "of doing nothing on the Border to address the Humanitarian and National Security Crisis" and accusing Mexico of being an "abuser" of the United States "for decades."

"We want action, not talk. They could solve the Border Crisis in one day if they so desired," Trump suggested.

On Saturday, Mexican President Lopez Obrador indicated that his country may tighten migration controls to help to address US concerns over the situation on the border, adding that Mexico City would also be looking to inform the US on what the country was already doing. Obrador added while Mexico did not plan to wage a trade war with the US, it did have a "plan" if Washington went ahead with the tariffs.

Mexico is one of the US's largest trading partners, with bilateral trade amounting to $671 billion in 2018, according to recent government figures. The US has a $72.7 billion trade deficit with its southern neighbour.