By Steve Holland and Dave Graham

LONDON/MEXICO CITY (Reuters) – President Donald Trump on Tuesday said he would probably order new tariffs on all Mexican goods imported to the United States next week despite a diplomatic push to avoid the levies, citing high flows of migrants entering the United States from Mexico.

Trump said last week Mexican goods would pay new tariffs beginning June 10 if Mexico did not halt a surge in the U.S-bound immigrants, mostly from Central America.

Mexico was preparing a proposal on immigration to present to U.S. officials at a meeting in Washington on Wednesday but Trump said the talks might not be enough.

“We’re going to see if we can do something, but I think it’s more likely that the tariffs go on,” Trump said at a news conference in London, describing large flows of migrants into America as an “invasion.”

“Mexico should step up and stop this onslaught, this invasion into our country,” Trump said, also calling on the U.S. Congress to pass immigration laws to address the situation and blaming Democrats for stalling any such effort.

Asked to comment on Trump’s remarks, Mexican President Andres Manuel Lopez Obrador told his regular morning news conference he was optimistic that a deal could be reached.

“The most important thing now is to reach an agreement,” Lopez Obrador said, indicating that he would continue to negotiate even if Trump did go ahead with the tariffs.

Before Trump spoke, Lopez Obrador told the two-hour news conference he expected Mexico to reach a deal with the United States over immigration ahead of the June 10 deadline.

“There are signs that it matters to the U.S. officials that there’s a deal,” he told his regular morning news conference.

The inflow of migrants, many asylum seekers escaping criminal violence in Central America, have long sparked Trump’s ire and helped fuel his successful bid for White House amid a campaign promise that he would make Mexico pay for a wall along the southern U.S. border. Efforts to get Mexico or U.S. lawmakers in Congress to fund the barrier have failed.

Trump’s tariff threat last week was aimed at pressuring Mexico, but it also spooked global markets and put a joint trade pact between the two countries and Canada further in doubt.

Despite Trump’s rhetoric, Mexico is now detaining double the number of migrants per day than a year ago, and three times as many as in January, when Lopez Obrador’s new government opted instead to give visas to Central Americans, hoping they would stay in Mexico.

Instead, most of them made their way to the border, contributing to the recent surge. Under pressure from the United States, the Mexican government changed strategy, and in May detentions surged past 20,000.

Lawmakers from Trump’s Republican Party have begun discussing whether they may have to vote to block the tariffs, according to a report by the Washington Post that cited people familiar with talks in Congress.

Trump said that sort of congressional action was unlikely. “I think if they do, it’s foolish.”  

Mexican Foreign Minister Marcelo Ebrard, in Washington for the talks with U.S. officials, said he hoped Wednesday’s meeting could be a starting point for negotiations. Mexican lawmakers and private sector officials will also be visiting Washington this week to press Mexico’s case, he added.

Mexican officials on Monday vowed to reject a U.S. idea to take in all Central American asylum seekers if it was raised at talks this week with the Trump administration.

“We’re going to find common ground, I think,” Ebrard said at a news conference.

(Reporting by Steve Holland In London and Dave Graham in Mexico City; Additional reporting by Jason Lange and Makini Brice in Washington and by Stefanie Eschenbacher in Mexico City; Writing by Jason Lange in Washington; Editing by Nick Zieminski and Alistair Bell)