A US federal judge has warned that he could hold the Trump administration in criminal contempt for violating his orders to turn around planes carrying deportees to El Salvador.
The comments are an escalation in a row which began last month when US District Judge James E Boasberg issued an order temporarily blocking the deportations.
However, lawyers told him there were already two planes with immigrants in the air - one headed for El Salvador, the other for Honduras.
Mr Boasberg verbally ordered the planes to be turned around, but the directive was not included in his written order. The Trump administration then denied refusing to comply.
On Tuesday, Judge Boasberg said he had found "probable cause" to hold the administration in criminal contempt.
He also warned he could refer the matter for prosecution if it does not "purge" its contempt by returning those sent to El Salvador to the US.
Charges could be brought forward by the Justice Department, NBC News reported.
However, that could create an uncomfortable situation for the department, which is headed by the attorney general - a position appointed by the president.
If the executive-led Justice Department refused to prosecute the matter, Judge Boasberg said he would appoint another attorney to prosecute the contempt.
The judge wrote: "The Constitution does not tolerate wilful disobedience of judicial orders - especially by officials of a coordinate branch who have sworn an oath to uphold it."
He gave the government a 23 April deadline.
White House director of communications Steven Cheung said the administration would seek "immediate appellate relief" - a review of a decision within a lower court before the case has been resolved.
Executive vs judicial
This marks a notable escalation in the ongoing tensions between the judicial and executive branches of the US government during Donald Trump's second term.
Parts of the US president's legislative programme have been halted by judges, as the administration strains against the restraints of the separation of powers.
Mr Trump previously called for Judge Boasberg to be impeached, while the Justice Department claimed he overstepped his authority - both reflecting the administration's attempts to overcome perceived obstacles to the implementation of its agenda.
Mr Trump's administration has also argued it did not violate any orders.
It claimed the judge didn't include a turnaround directive in his written order and said the planes had already left the US by the time the order came down.
Mr Trump took to social media ahead of the judge's words, claiming that former president Joe Biden allowed "millions and millions of criminals" into the US, adding: "Sorry but it's my job to get these killers and thugs out of here."
What could happen next?
Contempt is one of the ways judges like Judge Boasberg can take action to try and force the sitting administration to comply with rulings.
But what is criminal contempt?
According to the Cornell Law School: "Criminal contempt of court refers to disobedience of an order of the court which carries criminal penalties."
And what could happen next?
In his ruling, Judge Boasberg said he would identify the individual or individuals responsible for the noncompliance with his ruling, and they would be prosecuted, Sky News's US partner NBC News reported.
These charges, usually, would be brought about by the Justice Department.
However, being a department overseen by the president himself, this is perhaps a less viable option.
Judge Boasberg has already said he will appoint another attorney if the government department refuses to go ahead and prosecute.
A president can revoke criminal contempt by issuing a pardon, but civil contempt is not pardonable.
Meanwhile, long-standing precedent means the president cannot be held in contempt.
Judges are generally reluctant to hold US government litigants in contempt, but they have done so previously in the late 1990s and early 2000s.
If it came to it, and Judge Boasberg prosecuted an individual member of the administration, this option would quickly become complicated.
Federal contempt orders are enforced by US marshals - who are part of the executive branch.
If a president ordered a marshal not to enforce a contempt order against an executive branch official, it would violate the law.
David Noll, a professor at Rutgers Law School, noted in a recent Democracy Docket article that federal rules appear to allow judges, if needed, to bypass the marshals and hire other parties to enforce their contempt rulings.
The likes of local police and sheriffs are responsible to the court alone, NBC News said.
Nicholas Parillo, a professor at Yale Law School found that while district court judges are willing to issue contempt findings, sanctions are rarely upheld on appeal.
In short, the Trump administration could push this issue on untrodden legal ground.
'Administrative error'
Alongside the row is another over Kilmar Abrego Garcia, a man who was sent to El Salvador by the Trump administration in March despite an immigration court order preventing his deportation.
Washington acknowledged that Mr Garcia was deported due to an "administrative error".
The US Supreme Court has called on the administration to facilitate his return, upholding a court order by Judge Paula Xinis, but Trump officials have claimed that Mr Garcia has ties to the MS-13 gang.
Mr Garcia's lawyers have argued there is no evidence of this.
Democrat senator travels to El Salvador
Meanwhile, Democratic senator Chris Van Hollen arrived in El Salvador on Wednesday, saying he would seek a meeting with the country's officials to secure Mr Garcia's release.
"I just arrived in San Salvador a little while ago and look forward to meeting with the US embassy team to discuss Mr. Abrego Garcia's release," Mr Van Hollen said on social media.
He later said he met with the country's vice president, but not with Mr Garcia.
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This all comes after El Salvador's President Nayib Bukele visited the White House earlier this week.
During his time with Mr Trump, Mr Bukele said that he would not return Mr Garcia, likening it to smuggling "a terrorist into the United States."
Along with Mr Garcia, the Trump administration has deported hundreds of people, mostly Venezuelans, whom it claims are gang members without presenting evidence and without a trial.