Supporters of Pakistan's former Prime Minister Imran Khan in their thousands defied roadblocks to gather in Islamabad on Sunday.

The demonstration, led by Khan's Pakistan Tehreek-e-Insaf (PTI) party, is the largest in Islamabad since the retired international cricketer was jailed last year on several charges, some of them still before the courts.

The rally's "size and popularity ensure (PTI's) mobilization capabilities remain intact despite relentless attempts to curb it," said Michael Kugelman, Pakistan specialist at the Wilson Center, a U.S.-based think tank.

Protesters cleared Sunday containers used by Pakistani authorities to block major roads into Islamabad ahead of the demonstration.

"They closed the city with containers. But despite this, thousands are here. They cannot stop this motivation and emotions the people have right now," Humayun Mohmand, a PTI senator, told the Agence France-Presse (AFP).

In jail since August 2023, Khan insists along with his party that the charges against him are designed to prevent him from returning to office.

Backed by the military, which wields enormous influence, he rose to power in 2018 by standing against widespread corruption embedded in the country's revolving door of dynastic politics.

But he was ousted in 2022 after falling out with the military establishment.

That furthered a sense of helplessness and frustration among many Pakistanis who want the generals to stay out of politics in a country that has been ruled by the military on and off for much of its history, and where a civilian prime minister has never served a full term.

Khan's first arrest, on corruption charges in May 2023, sparked nationwide demonstrations by supporters expressing anger at the army. In response, the army orchestrated a massive crackdown on the PTI.