A high-level team of U.S. and Pakistani investigators grilled the father of the Times Square car bombing suspect and interrogated four people linked to a notorious Pakistani militant group, intelligence officials said Thursday.

The interrogators questioned Bahar Ul Haq in the northwestern Pakistani city of Peshawar. The retired senior Pakistani air force officer is the father of Faisal Shahzad, the 30-year-old Pakistani-American suspect in the case.

Ul Haq, who lives in the Peshawar suburb of Hayatabad, was not detained or arrested, the source emphasized.

Another official said the team was questioning four men suspected of having links to the banned militant group Jaish-e-Mohammed.

Banned in Pakistan, the group aims to unite the disputed territory of Kashmir with Pakistan and to expel foreign troops from Afghanistan, according to the National Counterrorism Center. It is also close to al Qaeda and the Pakistani Taliban. India and Pakistan have had disputes over Kashmir for decades.

(Read More: CNN)