By Asif Shahzad

ISLAMABAD (Reuters) -Former Pakistani prime minister Imran Khan on Tuesday was questioned by an anti-graft agency on corruption charges, his lawyer said, less than a week after he rejected a summons to appear and denounced the allegations against him.

The embattled Khan, who says corruption charges have been concocted, is embroiled in a confrontation with the powerful military, which has ruled Pakistan directly or overseen civilian governments throughout its history.

Khan was arrested and detained on May 9 in the same case, sparking widespread protests by his supporters, and raising new worries about the stability of the nuclear-armed country as it struggles with its worst economic crisis in decades.

Khan was later freed on bail.

"He has joined investigation," said his lawyer, Faisal Chaudhry, referring to his questioning by officials of the National Accountability Bureau (NAB) on charges that he and his wife received land worth millions of dollars as a bribe from a real estate tycoon through a charitable trust.

Khan called the allegations "absolutely false, frivolous and concocted" in a statement to NAB last week.

The former international cricket star became prime minister in 2018 with the tacit support of the military, though both sides denied it at the time, but he later fell out with generals and was ousted as prime minister after losing a confidence vote in 2022.

Khan, 70, has since then been campaigning for a snap election, with rallies with his supporters across the country.

The prime minister who replaced him, Shahbaz Sharif, has rejected Khan's call for a general election before it is due late this year.

The graft case is one of dozens registered against Khan in the last year. He says there are close to 150 cases in total, and that the charges are part of an attempt by the government and military generals to sideline him and his party from politics.

The government and military deny this, but recent protests against his arrest saw his supporters ransacking the homes of senior officers and storming army headquarters, posing an unprecedented challenge to the Muslim country's most powerful institution.

His party, which denies orchestrating the violence, has also faced a crackdown following the protests.

Most of the top leaders of Khan's party - the Pakistan Tehreek-e-Insaf (PTI) - have been taken into custody, while many have quit the party or politics entirely amidst the crackdown in the wake of the violent protests.

"We had all heard about forced marriages in Pakistan but for PTI a new phenomenon has emerged, forced divorces," Khan said on Twitter referring to the alleged pressure being applied by the government and military on his party members to leave his side.

On Tuesday, the party saw its highest profile exit when former Minister for Human Rights Shireen Mazari - who had been in custody for over 10 days - announced in a press conference that she was leaving politics due to health and family reasons.

(Reporting by Asif Shahzad and Gibran Peshimam; Writing by Miral Fahmy; Editing by Robert Birsel, William Maclean)