Islamabad: The new chiefs of ISI and Pakistan Air Force on Monday assumed office, a day ahead of a crucial parliamentary session that will determine the contours of future relations with the US.

Lt Gen Zahir-ul-Islam went to the ISI headquarters at Aabpara here to take charge as the new Director General of the powerful spy agency.

He replaced Lt Gen Ahmed Shuja Pasha, who completed his tenure on Sunday. Pasha had been given two extensions after he reached the age of retirement in 2010.

Islam had earlier served as a Deputy Director General in the ISI as a major general.

He was subsequently promoted to the rank of lieutenant general and made the commander of the Karachi Corps.

He belongs to the 13 infantry unit of Punjab Regiment and had earlier as General Officer Commanding for Murree.

Meanwhile, Air Marshal Tahir Rafique Butt took over as the new chief of the Pakistan Air Force at a ceremony held here at Air Headquarters here.

Outgoing Air Chief Marshal Rao Qamar Suleman formally handed over the PAF's sword of command to Butt. The outgoing and incoming air force chiefs were presented separate guards of honour to mark the change of command.

Born in 1955, Butt graduated from the PAF Academy at Risalpur in March 1977.

After his fighter and operational conversion courses, he flew various types of combat jets and training aircraft.

He is a qualified flying instructor and a combat commander, and has commanded a fighter squadron, a fighter flying wing and two airbases.

Butt earlier served as Deputy Director Plans, Director Flight Safety, Assistant Chief of Air Staff (Personnel). Before taking over as PAF chief, he served as the vice chief.

The senior officers took over the key positions a day before a joint session of the Senate and National Assembly convened by President Asif Ali Zardari to define new terms of engagement with the US.

Prime Minister Yousuf Raza Gilani had ordered the parliamentary review after a cross-border NATO air strike killed 24 Pakistani soldiers in November last year.

(Agencies)