WASHINGTON – President Donald Trump said Friday there is a good chance the U.S. and Mexico will reach a deal to avoid new tariffs on Mexican imports, but he warned that the duties will take effect as planned on Monday if the two sides are unable to strike an agreement.

"If we are able to make the deal with Mexico, & there is a good chance we will, they will begin purchasing Farm & Agricultural products at very high levels, starting immediately," Trump tweeted. "If we are unable to make the deal, Mexico will begin paying Tariffs at the 5% level on Monday!"

The two countries began a third day of high-stakes discussions on Friday in hopes of reaching a deal to avoid the duties.

Trump has threatened to slap 5% tariffs on all Mexican imports, starting Monday, unless the Mexican government stops the flow of Central American migrants coming to the U.S. southern border. He has vowed to hike the tariffs 5 percentage points per month, until they reached 25%.

An aide to Vice President Mike Pence said the administration will on Friday submit a legal notification of tariffs to take effect Monday – but could just as easily pull it back over the weekend if negotiations continue to go well.

Marc Short, Pence's chief of staff, told reporters: "There's a legal notification that goes forward today with a plan to implement tariffs on Monday, but I think there is the ability – if negotiations continue to go well – that the president can turn that off at some point over the weekend."

The biggest flashpoint in the U.S.-Mexico negotiations over tariffs and immigration revolves around asylum – specifically which country should be responsible for absorbing the desperate migrants fleeing poverty and violence in Central America.

The Trump administration wants Mexico to agree to take almost every asylum seeker that crosses into Mexico – pushing the Mexican government to sign an agreement that would essentially bar Central American migrants from trying to gain asylum in the United States.

Mexican President Andres Manuel Lopez Obrador has resisted that step so far, although there were signs Thursday that Mexican negotiators might relent.

If that happens, the U.S. and Mexico could sign a little-known treaty – called a safe third-country agreement – that would carry huge implications for immigration in both countries.

“That’s probably the most important demand that we have of Mexico,” said Mark Krikorian, executive director of the Center for Immigration Studies, a think tank that favors stronger limits on immigration.

Migrants generally must seek asylum in the first country they reach after fleeing their homeland – but only if that country is considered safe. If it’s not safe, migrants can pass through – as they’re doing in Mexico right now – and apply in the next country they reach, in this case the United States.

If Mexico agrees to be designated as a safe third-party country, the U.S. could deny the asylum claims of virtually all the Central American migrants now seeking refuge in the U.S.

American immigration authorities could “turn them around and send them back” to Mexico, Krikorian said. He has accused Mexico of being an “asylum free rider” by enacting liberal asylum laws but steering most refugees to the U.S. border.

Designating Mexico as a safe asylum country “would really take away most of the incentive” for migrants to trek across Mexico to the U.S. border, Krikorian said.

But immigration advocates say Mexico’s asylum system is already overwhelmed, and the country is not safe – particularly for vulnerable migrants. Trump’s own State Department has advised Americans not to travel to five Mexican states, citing rampant and often violent crime.

“Robberies, extortion, kidnapping ... these are common situations,” said Aaron Reichlin-Melnick, a policy analyst with the American Immigration Council, an advocacy group devoted to stronger protections for immigrants.

The council recently conducted a survey of migrant mothers detained in Mexico, and 90% said they did not feel safe. Nearly half of the 500 women said that they or their child had been robbed, sexually assaulted, threatened or subject to other harm.

“The Mexican police and state agencies charged with providing security are often the very actors robbing migrants, charging them fees in order to pass, or handing them over to criminal groups who tax or victimize migrants,” Stephanie Leutert, director of the Mexico Security Initiative at the University of Texas, wrote in a 2018 analysis of the issue.

She and others note that Mexico has already moved to take in more refugees. Asylum requests have increased each of the past five years, with the nation on track to reach nearly 60,000 in 2019, nearly double the number from the year before, according to data from the Mexican Commission for Refugee Assistance.

Leutert said Mexico’s government institutions are too weak to absorb more migrants than they’re already taking in.

“I think the U.S. should be working with Mexico more on these issues and not pushing all this enforcement onto a country that doesn’t” have the resources to handle it, she said in an interview.

Krikorian says the U.S. might need to offer Mexico financial assistance in exchange for an asylum agreement.

“I think we should combine carrots along with the sticks,” he said, referring to President Trump’s threat to impose tariffs on all Mexican imports if the Obrador government does not stop the flow of migrants.

Indeed, Obrador has called for the U.S. to help Mexico address the root causes of the migrant crisis – urging the Trump administration to help foot the bill for economic development and other initiatives aimed at relieving the crippling poverty and corruption in Guatemala, Honduras and other Central American countries.

“The U.S. stance is centered on immigration control measures, while our focus is on development,” Roberto Velasco, a spokesman for the Mexican Foreign Ministry, tweeted on Thursday evening. “We have not yet reached an agreement but continue to negotiate.”

Mexico’s Foreign Secretary Marcelo Ebrard declined to comment Thursday on the prospect of a safe third-country agreement. And the White House did not respond to questions about the Trump administration’s demands for that.

But Krikorian said a fat financial aid package could go a long way in persuading Mexico to accede to Trump’s demand.

“We can make it worth Mexico’s while, in combination with a stick that if they don’t take our more money that they’re going to suffer some consequences,” he said.

Even before Trump’s threatened tariffs become official, Mexico has been taking action to assuage his demands that migration through Mexico stop.

Ebrard has confirmed 6,000 members of the national guard will be sent to southern states such as Chiapas, which shares a porous border with Guatemala.

Mexico’s Finance Ministry on Thursday froze the accounts of 26 unnamed individuals it accuses of financing human trafficking and the caravans, which crossed the country last fall.

The federal prosecutor's office also detained two prominent members of Pueblo Sin Frontera, a bi-national migrants’ rights group, which convenes and coordinates caravans transiting Mexico. Pueblo Sin Frontera blasted the arrests as part of pattern of persecution and the “criminalization” of attempts at providing humanitarian assistance to migrants.

Mexican immigration officials and navy marines corralled a caravan earlier this week in Chiapas, barely eight miles from the border with Guatemala.

Trump's threat of tariffs comes at an inopportune time for Mexico. The economy has slumped and the central bank has cut its 2019 growth projects to a range of 0.8 percent to 1.8 percent.

“It's very unfortunate timing as concerns surrounding decelerating economic growth and fiscal policy direction have materialized in the last few months,” said Horacio Coutiño, a financial analyst in Mexico City.

Contributing: Alan Gomez, David Jackson, David Agren