ISLAMABAD: Pakistani police detained hundreds of supporters of ousted prime minister Imran Khan overnight ahead of a major sit-in planned by the former leader, senior party members and police sources said Tuesday, as the government pledged to block the protest.

Khan, alleging he was removed through a "foreign conspiracy", plans to lead tens of thousands of supporters from his power base in the northwestern city of Peshawar to the capital Islamabad demanding fresh elections.

"Tomorrow I will be leading the largest march of Pakistan's history. I don't consider it politics but jihad," Khan said.

Security was being built up across the country, with shipping container roadblocks hauled into place in Islamabad and the government quarter put on lockdown, while many entry and exit points around the city of Lahore -- around 380 kilometres (236 miles) away -- were also blocked.

PTI's long march will not be allowed to enter Islamabad: Rana Sanaullah

"This (protest) is being done to divide the nation and promote chaos," Interior Minister Rana Sanaullah told reporters. "Nobody should be allowed to besiege the capital and dictate his terms."

"This march cannot be allowed to take place," Information Minister Marriyum Aurangzeb added.

Opposition arrests

Two police officials told AFP that more than 200 supporters of Khan's Pakistan Tehreek-e-Insaf (PTI) party were arrested in overnight raids in the nation's most populous province Punjab.

They were booked on public order offences and remain in detention, one of the sources said.

Fawad Chaudhry, the former information minister in Khan's government, accused police of not having the necessary warrants and put the number of arrested at more than 400.

Imran Khan's long march not against govt, but establishment: Maryam Nawaz

"More than 1,100 houses were raided overnight. Police entered the houses without any warrants and insulted women and children," he tweeted.

One police officer was shot dead during a raid on a PTI supporter's house in Lahore, Punjab Chief Minister Hamza Shahbaz Sharif said.

Police have not officially commented on the arrests or allegations.

Attaullah Tarar, a senior leader in new Prime Minister Shehbaz Sharif's PML-N party, said at a press conference that protestors had been planning to join the march "with weapons".

"We have information that they have started collecting ammunition at various places," he told reporters.

Imran Khan plans to bring 'armed men' to Islamabad: Marriyum

On Saturday, senior PTI leader and former minister Shireen Mazari was arrested near her house in the capital over a decades-old land dispute. She was briefly detained before a court ordered her release.