Pakistan’s former prime minister Imran Khan, who is facing corruption charges, says he will not join an investigation by the powerful anti-graft agency while he was out on bail.

The National Accountability Bureau (NAB), which has in the past investigated, put on trial and jailed all those who have served as prime minister since 2008, had earlier summoned Mr Khan for investigation into the graft charges, a spokesman said.

Khan was arrested on the charges, which he denies, on May 9 and later set free on court-ordered bail that was extended to May 31.

In a statement addressed to the NAB’s deputy director, and shown to Reuters by one of Mr Khan’s lawyers, the former prime minister called the allegations against him “absolutely false, frivolous and concocted”.

He said he was in the process of applying for, and obtaining, bail in a number of other legal cases and would not be available before his protective bail expired on May 22.

Mr Khan’s arrest triggered a wave of violence that deepened political instability in the South Asian nation of 220 million.

Pakistan has also been facing its worst ever economic crisis, with critical IMF funding needed to avert a balance of payment crisis delayed for months.

His wife Bushra Khan, commonly known as Bushra Bibi, is also on bail until May 23.

On Wednesday, Mr Khan said that police had surrounded his house in Lahore, in Punjab province, and that he expected to be re-arrested soon, after the government warned him to hand over supporters who it blamed for attacks on the army.

Punjab’s information minister Amir Mir said the government did not have any plans to arrest Mr Khan as he had been given bail by court.

“All we want him to hand over the terrorists hiding at his home,” he said.

Mr Khan has said authorities could search his home but only with legal warrants from a court, and has denied sheltering anyone involved in the violence.

On Thursday, Mr Khan’s aide Iftikhr Durrani allowed journalists into some areas of Mr Khan’s Lahore home to “look for terrorists”.