A joint investigation team has arrived at the Attock Jail to interrogate PTI chief Imran Khan over May 9 events, sources said.

The JIT from Lahore led by Imran Kishore arrived at Attock Jail, established 100 years ago on the outskirts of historical Attock city, around 60 kilometres (40 miles) west of the capital, Islamabad.

The security outside the prison has further been tightened by the jail administration.

Violent protests broke out on May 9 when Khan was arrested within the premises of Islamabad High Court in a graft case. Many protesters attacked state buildings and military installations, which was condemned by the government and the PTI.

The previous government blamed the Khan-led party for the protests and claimed that former prime minister instigated his party workers against state institutions.

Last month, a special prosecutor told an antiterrorism court that a joint investigation team found PTI Chairman Imran Khan guilty of abetment and other charges in the May 9 incidents.