Texas troopers use pepper spray to disperse protesters outside a detention facility in Dilley, Texas, on Wednesday.

The United States administration warned Minneapolis Mayor Jacob Frey on Wednesday that he was "playing with fire", after the mayor said the city would not enforce immigration laws.

"Could somebody in his inner sanctum please explain that this statement is a very serious violation of the law, and that he is playing with fire!" President Donald Trump posted on social media.

In response, Frey wrote, "The job of our police is to keep people safe, not enforce fed immigration laws."

The exchange came despite the president saying his administration would "de-escalate a bit" in the city.

Tensions remained high in Minneapolis, where observers and activists said immigration raids had not slackened but appeared to be more targeted, despite Trump having said after a second fatal shooting that the administration would reduce the number of Border Patrol officers.

The city has been roiled by unrest, including confrontations between protesters and immigration agents, resulting in two US citizens being shot dead by federal agents.

The fatal shooting of Alex Pretti, 37, raised tensions further between state and federal officials, who had already been at odds with the US administration over the shooting death of Renee Good on Jan 7.

Department of Homeland Security spokeswoman Tricia McLaughlin said two Border Patrol agents who fired their guns in the fatal shooting of Pretti have been placed on administrative leave.

Mayor Frey said the city police officers are overwhelmed. With both protesters and federal agents alike calling 911 for help, officers across the region have struggled to respond.

Police and union officials said the morale has plummeted as officers find themselves caught between powerful political forces beyond their control, The New York Times reported.

"Both sides dug their heels in, and here we are in the middle of it," said Mark Ross, president of the St. Paul Police Federation. "They are playing political football and we are the ones getting kicked around."

The administration's border czar, Tom Homan, met with Minnesota Governor Tim Walz on Tuesday, looking for ways to lower the temperature between federal and state authorities. Homan was set to present his plans on Thursday as the new face of the immigration crackdown in Minneapolis.

Saturday's fatal shooting of Pretti was widely condemned across the political aisle despite initial efforts by White House officials to justify the killing.

Senate Democrats laid out a list of demands on Wednesday for the Department of Homeland Security, including an enforceable code of conduct for federal agents conducting immigration arrests. They have pledged to block a spending bill unless their demands for reforms are met.

Senate Democratic leader Chuck Schumer said on Wednesday that the legislation would not pass until US Immigration and Customs Enforcement is "reined in and overhauled".

With no serious negotiations underway, a partial shutdown appeared increasingly likely starting Saturday.

Meanwhile, Republicans are increasingly concerned that immigration enforcement is becoming a political liability in the upcoming midterm elections.

"This is about regaining the trust of the American people on this issue, and I really think we're losing on an issue that we should be winning on," Senator Thom Tillis told reporters on Capitol Hill.

Agencies contributed to this story.

shiguang@chinadailyusa.com