Pakistan summoned a senior US diplomat here and lodged a strong protest over America's alleged "interference" in its internal affairs, according to media reports on Friday.

The US State Department on Thursday firmly rejected embattled Prime Minister Imran Khan's remarks over Washington's role in an alleged foreign conspiracy to oust him from power.

In a live address to the nation, 69-year-old Khan discussed a 'threat letter' and termed it as part of a foreign conspiracy to remove him as he was not acceptable for following an independent foreign policy. He named the US as the country behind the threat letter in what appeared to be a slip of tongue.

Dunya News quoted sources as saying that the US diplomat was summoned by the Foreign Office (FO) over a threatening letter that warned of dire consequences if the Opposition's no-confidence motion against Khan failed.

The step was taken after a decision by Pakistan's National Security Council (NSC) on Thursday.

The Foreign Office also handed over a letter of protest to the US diplomat over the language used by a foreign official during a formal communication.

The US diplomat has been told that "interference in Pakistan's internal affairs is unacceptable", the report said.

The NSC decided to issue the strong demarche to the country that, in an interaction, expressed displeasure at Pakistan's policy on Ukraine and subsequently Pakistan's Ambassador to the US Masood Khan sent a letter to the Foreign Office on the issue.

Prime Minister Khan linked the letter with the no-confidence motion against him by the Opposition in the National Assembly. The National Assembly is scheduled to vote on the no-trust motion on Sunday.

Khan's address came at a critical juncture of his political career when he lost majority after defection from his Pakistan Tehreek-e-Insaf (PTI) party. Two of his allied parties also withdrew their support and joined the ranks of the Opposition.

The US has asserted that it did not send any letter to Pakistan on the current political situation in the country as it sought to refute allegations of America's involvement in the no-confidence motion against the Imran Khan-led government.

Khan met President Vladimir Putin in the Kremlin on February 24, the day the Russian leader ordered a "special military operation" against Ukraine. Khan also became the first Pakistani premier to visit Russia in 23 years after former premier Nawaz Sharif travelled to Moscow in 1999.