In a letter to colleagues, the Democratic House Majority leader said she and Joint Chiefs of Staff Mark Milley had discussed the “available precautions for preventing an unstable president from initiating military hostilities or accessing the launch codes and ordering a nuclear strike”.

“The situation of this unhinged President could not be more dangerous, and we must to everything that we can to protect the American people from his unbalanced assault on our country and our democracy,” she wrote.

The extraordinary intervention came as Democrats tried to ramp up pressure on Vice-President Mike Pence to invoke the 25th Amendment to remove the president from office, after a pro-Trump mob stormed the Capitol building on Wednesday.

Five people including a Capitol Police officer have now died following the riot. Mr Trump held a rally near the White House earlier in the day and has been accused of inciting the violence after urging his supporters to march on Capitol, where lawmakers has gathered to certify Joe Biden’s presidential election victory.

Three House Democrats are planning to introduce articles of impeachment against Mr Trump on Monday. But in her letter, Speaker Pelosi reiterated her preference that Republicans take responsibility for removing their own president from office.

"As you know there is growing momentum around the invocation of the 25th Amendment, which would allow the Vice President and a majority of the Cabinet to remove the President for his incitement of insurrection and the danger he still poses.