Pakistan's Prime Minister Imran Khan claimed that some people in the country were conspiring to topple his government and that the plot had foreign backing, in a vague reference to the powerful military that once supported him.

"We received a threat in writing and I have the evidence," Khan said during a speech for party supporters at a rally in the capital.

In a carefully worded statement that he read out at the end of his two-hour address, Khan said that he had been asked to step down in the "national interest" but did not provide any further details.

"We will not compromise on national interest," Khan said.

Khan added he knew that people acting at the behest of foreign forces wanted to topple his government and that he was aware of all the details and would soon make them public.

Meanwhile, tens of thousands of activists from Khan’s Pakistan Tehreek-e-Insaaf (PTI) party marched to Islamabad in a show of support ahead of a vote of no confidence that is expected next week.

Khan, who faces defections from his party, said he was "hopeful" that he would win the vote.

His rally was organized in the face of similar demonstrations held by opposition groups to put him under pressure.

An opposition alliance led by the party of former premier Nawaz Sharif accuses Khan of governing poorly and began a process on March 8 that could lead to his ouster.

No Pakistani prime minister has ever completed a term in office. Khan's is due to run through August 2023.

Khan came to power in 2018 in national elections that were tainted by allegations that he was supported by the country's powerful military.