ISLAMABAD

Thousands of ruling party and opposition supporters have descended on Pakistan's capital in a show of power on Sunday ahead of a no-confidence vote against beleaguered Prime Minister Imran Khan.

Khan's Pakistan Tehreek-e-Insaf (PTI) party is set to hold what it says "the biggest rally ever" in Islamabad, which will be addressed by the premier himself who is facing the toughest moment of his three-and-a-half-year stint.

The party contends that over 1 million people will attend the rally, a claim political observers doubt regarding the capacity of the venue.

Khan, who is a facing a daunting no-confidence vote of the allied opposition, has been in the public for over two weeks, holding rallies and meetings across the country.

PTI workers have started turning up in the capital city from different parts of the country to reach the Parade Ground, near the parliament building, the venue of the party's power show.

The opposition, for its part, has also set off its "long march" in the capital, and plans to hold a counter rally on Monday.

Thousands of opposition supporters have gathered at Kashmir Highway and the Faizabad junction, a gateway to the capital, blocking the two sites from traffic.

The Interior Ministry has deployed over 15,000 paramilitary troops and police to avert any clash between the rival activists.

Maryam Nawaz, the daughter of three-time Prime Minister Nawaz Sharif, is leading a march in the northeastern Punjab province to join the opposition rally in Islamabad.

Opposition parties filed the motion earlier this month, claiming Khan has lost his parliamentary majority.

It is said that defection of dissident lawmakers and suggestions that coalition partners may join the opposition has left Khan short of the minimum 172 needed for a simple majority in the parliament.

But the allies, Pakistan Muslim League -Quaid-I-Azam, Balochistan Awami Party and Muttahida Quami Movement, remain undecided whether to support or oppose the no-confidence motion.

The government has also filed a court petition to determine if dissident votes against the prime minster can be declared invalid.

Under the law, parliamentarians who defect could lose their seats if they choose to vote against their party.​​​​​​

Khan claims to have a "surprise" for the opposition, and has said he will emerge victorious.

Voting on the no-confidence motion is expected this coming week.