PML-N workers and police clashed on Tuesday outside a National Accountability Bureau (NAB) office in Lahore where party leader Maryam Nawaz had arrived to record her statement in a case related to "illegal" acquisition of land in Raiwind.

The scene outside the building turned violent when the PML-N leader's caravan, which included several cars and hundreds of supporters on foot, reached outside the NAB premises on Multan road.

Television footage showed men in plain clothes pelting stones at law enforcers, who were also seen assaulting some PML-N workers with batons, water cannons and tear gas. Several television channels also showed footage and pictures of cars, purportedly part of the PML-N caravan, laden with bags full of stones.

Dozens of party workers were also seen being taken into custody by police from the site. According to the PML-N spokesperson, at least 50 workers were arrested by police during the clash.

As the situation outside the watchdog's building turned violent, Maryam, who was in one of the vehicles part of the caravan and surrounded by supporters, posted a video of her car's broken windshield and alleged that "police had pelted her car with stones [as a result of which] the glass had cracked".

In another tweet, she condemned police brutality against PML-N party workers. "I strongly condemn police shelling, use of tear gas and lathi charge on peaceful party workers who came to show solidarity with me," she said.

She also shared pictures of party workers who were injured in the clash.

Speaking to reporters, Maryam said she would not leave without recording her statement and that NAB should not have summoned her if they did not have the courage to listen to her replies.

"If you do not have the courage, you should have thought it through before calling me here. After calling me, you turn to shelling and pelting stones on innocent PML-N workers. If I did not have a bullet proof car, think of how much damage would have been caused."

Maryam said she was advised to get pre-arrest bail to save herself from NAB's "black tactics" but she chose not to.

"I am getting messages from NAB to leave but I am standing here. If you have brought me here on false allegations, listen to my answers as well. If you have questioned, then have the courage to listen to my answers," she added.

Later, she left after NAB said in a press release that her hearing had been postponed.

'Organised hooliganism by PML-N workers'

In its statement on the incident, NAB said Maryam had been summoned in a "personal capacity" to record her statement but instead of appearing, "she displayed hooliganism in an organised manner through PML-N workers by pelting stones and creating disorder".

"Such an attitude has been seen against a constitutional and national institution for the first time in 20 years in which not only windows of the building were broken by throwing stones but employees were also injured," the statement said.

The bureau said it was "immediately suspending Maryam's appearance", adding that it "strongly condemned that PML-N workers and various miscreants had tried to interfere in legal proceedings in an organised manner".

The statement added that on NAB Chairman Justice (r) Javed Iqbal's instructions, it has been decided that a first information report (FIR) will be filed against PML-N leaders and workers for "interfering with the state's work".

"NAB is a national institution and it is only affiliated with the country and the people. NAB does not have connections with any political party or group and all its activities are conducted according to the Constitution and the law," the statement said.

Later, the accountability bureau filed an application for registering a case against Maryam and other senior party leaders at the Chuhang Police Station.

The application, signed by the deputy director of intelligence and security at NAB, Lahore, stated that this was the first time in the bureau's 20-year history that a constitutional and legal department was treated in such a "heinous" manner.

It claimed that the incident was carried out after planning by Maryam and her husband, retired Capt Mohammad Safdar Awan, alongside party workers, adding that vehicles full of stones were brought from Jati Umrah.

It added that on Maryam's provocation, party workers gathered outside the office, adding that they resorted to pelting police officials with stones when they were asked to disperse.

'PML-N workers threw stones to put pressure'

Speaking to GeoNews, Punjab Law Minister Raja Basharat claimed PML-N party workers threw stones to put pressure on the anti-graft watchdog, adding that it was not "appropriate" for Maryam to say that she was the one who was targeted when video footage showed the opposite.

He maintained that action will be taken against the culprits responsible, stating that no one can be allowed to take the law into their own hands. "Action will be taken against those who can be identified through video footage," he said.

'Shocking, condemnable behaviour'

PPP Chairperson Bilawal Bhutto-Zardari took to Twitter to denounce the incident. "Condemn the unnecessary use of force, teargas and stone pelting on Maryam Nawaz and her party workers by police in Lahore today," he tweeted.

PML-N leader Ahsan Iqbal said that he strongly condemned the "worst torture and arrests of peaceful party workers by NAB and the government".

PPP Senator Sherry Rehman tweeted: "Shocking and condemnable behaviour by Punjab police at Maryam Nawaz’s vehicles at the NAB premises. What messages being given out? That even the security of political opponents of this regime is under threat?"

Earlier this month, NAB had issued a call notice to Maryam asking her to appear before a combined investigation team on Aug 11 (today) and bring details of 1,400 kanals she allegedly acquired in Raiwind in 2013 in violation of rules/law.

The bureau also sought details of sources of funds for the purchase of the land and the taxes and duties paid on it. "Provide details of the use of the land, whether it is being used for agriculture cultivation or for any other commercial activity," NAB said.