Islamabad: Pakistan's Foreign Ministry on Thursday lodged a formal protest with the US over the alleged 'threat letter' that called for the resignation of Prime Minister Imran Khan, local media reported.

The acting US envoy in Islamabad was summoned to the Foreign Ministry over the "threatening" letter, hours after the country's top decision-making body on national security voiced concerns over the issue during a meeting chaired by Prime Minister Imran Khan, Express Tribune reported.

A Pakistan Foreign Office official confirmed that a demarche was also handed over to the acting US envoy, adding that the US was told that the use of such undiplomatic language was unacceptable, the report said.

"As decided in the National Security Committee (NSC) meeting held on 31 March 2022, the requisite demarches have been made through diplomatic channels," the Foreign Office spokesperson said in a statement in the early hours of Friday.

The NSC meeting was attended by federal ministers for defence, energy, information, interior, finance, human rights and planning, besides the chairman of the Joint Chiefs of Staff Committee, services chiefs, national security adviser and senior officers, the report said.

The NSC meeting was convened against the backdrop of an alleged "foreign-funded plot" against the ruling Pakistan Tehreek-e-Insaf (PTI) government. The presence of the alleged plot was based on a diplomatic cable the Pakistani ambassador in Washington wrote to the Foreign Office earlier this month, the report said.

In an address to the nation on Thursday, Pakistan's embattled Prime Minister Imran Khan had raised a "foreign conspiracy" charge amid the opposition's growing confidence about the no-trust motion against his government that is pending in the National Assembly.

"The United States", Imran Khan said in a slip of the tongue and then stated that "a foreign country" had sent a "threatening memo" which was against the Pakistani nation.

"On March 8 or before that on March 7, the US sent us a...not the US but a foreign country sent us a message. The reason why I talking about this...for an independent country to receive such a message... this is against me and the country," he said.

Later in the day, the United States rejected insinuations made by Pakistan Prime Minister Imran Khan regarding Washington's role in the alleged "foreign conspiracy" to oust him from power.

"There is no truth to these allegations. We are closely following developments in Pakistan. We respect and support Pakistan's constitutional process and the rule of law," a US State Department spokesperson told ANI.

Khan had waved the "letter" at a public rally on March 27 and said there was a foreign conspiracy to oust him. He had sought to link the opposition's no-confidence motion with a "foreign-funded" move to topple his government.

Pakistan media reports said that letter is the word-for-word transcript of a conversation between the diplomats of Pakistan and another country sent to Pakistan's Foreign Ministry.

In Pakistan's National Assembly, the no-trust vote against the Imran Khan government was deferred to April 3. The proceedings of the National Assembly were adjourned till April 3 soon after it met on Thursday to discuss the no-confidence motion.

Earlier, on Monday, Pakistan Muslim League (PML-N) President Shahbaz Sharif tabled the no-confidence motion.

Imran Khan is the third Prime Minister to face the no-confidence motion in Pakistan.

After the no-confidence motion was tabled with a total of 161 votes in favour, the proceedings of the National Assembly were adjourned till March 31.

Imran Khan received a massive blow when the PTI "lost the majority" in the National Assembly after losing its key ally in the coalition Muttahida Qaumi Movement Pakistan (MQM-P). The MQM announced on Wednesday that it had struck a deal with the opposition Pakistan People's Party (PPP) and would support the no-trust vote in the 342-member National Assembly.

The government's survival depends on the support of allies such as MQM-P (7 seats), BAP (5 seats), PML(Q) (5 seats), GDA (3 seats), AML (1 seat), JWP (1 seat) and two independents.