ISLAMABAD Pakistan police imposed an emergency order banning gatherings as supporters of Imran Khan were expected to march to the capital on Friday where the former prime minister will appear for a court hearing.

His arrest earlier this week, which sparked deadly unrest in the nuclear-armed nation, was ruled "invalid and unlawful" by the Supreme Court on Thursday.

Khan's Pakistan Tehreek-e-Insaaf (PTI) party said thousands of "peaceful Pakistanis" from across the country will gather in Islamabad in solidarity with their leader.

Khan, 70, an international cricket hero-turned-politician, will appear before the Islamabad High Court at 11 a.m. (0600 GMT) for a hearing on his petition challenging the anti-corruption action against him, on orders of the top court.

His arrest aggravated instability in the country of 220 million people at a time of severe economic crisis - with record high inflation, anaemic growth and a delayed IMF funding - and escalated Khan's tussle with the powerful military.

Nearly 2,000 people have been arrested so far and at least eight killed after Khan's supporters clashed with police, attacked military establishments and set other state buildings and assets ablaze, prompting the government to call in the army to help restore order.

The army has warned Khan's supporters that it will respond firmly if there are further attacks on its assets, saying in a statement on Wednesday that the violence on its installations was "pre-planned" and ordered by his party leadership.

Khan, who opponents say was brought to power through a rigged election in 2018 by the generals, has blamed the military for his ouster from office in April 2022 in a parliamentary no-confidence vote.

The army, which remains Pakistan's most powerful institution, having ruled it directly for close to half its 75-year history through three coups, has denied Khan's allegations.

(Writing by Shivam Patel; Editing by Raju Gopalakrishnan)