Thousands of Pakistani Islamists opposed to the country's anti-terror alliance with Washington converged on Islamabad on Monday after a "long march" to protest over the reopening of NATO supply routes to Afghanistan.

Around 15,000 protestors gathered outside the Pakistani parliament to chant anti-US slogans and wave the banners of the Defence of Pakistan Council, a coalition of right wing and hardline Islamist groups which organised the protest march from the eastern city of Lahore.

Islamabad agreed to reopen overland routes to NATO convoys last week after a seven-month blockade sparked by a botched US air raid on a border post that killed 24 Pakistani soldiers.

The Defence of Pakistan coalition has attracted large turnouts at recent rallies across the country, which some see as a build up to the formation of a political party to contest the next general election, widely expected within the next year.

Coalition chairman Maulana Samiul Haq told a rally on Sunday before the convoy of buses, trucks and cars left Lahore on the 275-kilometre (170-mile) journey to the capital that the movement would continue until Islamabad severed all ties with the US and NATO.

Outside parliament on Monday evening the crowd chanted slogans including "Death to the USA" and one speaker called for the arrest of the CIA chief in Pakistan.

Earlier on Monday, gunmen killed six soldiers and a police officer at a camp close to Islamabad hours after the march had passed through the area.