House Speaker Paul Ryan warned the White House on Tuesday against firing special counsel Robert Mueller before he completes his investigation into possible Trump campaign collusion with Russia.
"The special counsel should be free to follow through with his investigation to its completion, without interference," the top Republican in the House of Representatives said.
"I am confident that he will be able to do that. I received assurances that his firing is not even under consideration," Ryan told reporters.
"We have a system based on the rule of law in this country. We have a justice system and no one is above that justice system."
President Donald Trump is reported to have considered firing Mueller -- who is focusing on Trump, his close aides and family -- although White House lawyer Ty Cobb denied that was the case on Sunday.
Mueller is probing whether the Trump campaign joined in Russian efforts to interfere with the 2016 presidential election -- efforts that sought to boost Trump's chances of winning, according to US intelligence.
He is also investigating whether Trump may have illegally tried to obstruct the probe.
In recent weeks Trump has reportedly been increasingly agitated by Mueller's 10-month-old investigation.
"The Mueller probe should never have been started in that there was no collusion and there was no crime," he tweeted at the weekend, taking aim at Mueller directly for the first time.
He also accused the special counsel's team of being loaded up with Democrats.
Republican Senator Lindsey Graham also warned against firing Mueller Sunday.
"If he tried to do that, that would be the beginning of the end of his presidency," Graham said.