ISLAMABAD – A passenger jet that officials suspect veered off course in monsoon rains and thick clouds crashed into hills overlooking Pakistan’s capital Wednesday, killing all 152 people on board.

The Airblue jet’s crash was the deadliest ever in Pakistan, and just the latest tragedy to jolt a country that has suffered numerous deaths in recent years from al-Qaida and Taliban attacks. At least two U.S. citizens were on the plane, which carried mostly Pakistanis.

The plane left the southern city of Karachi at 7:45 a.m. for a two-hour flight to Islamabad and was trying to land when it lost contact with the control tower, said Pervez George, a civil aviation official. Airblue is a private airline based in Karachi, Pakistan’s largest city.

The aircraft, an Airbus A321, crashed about 9 miles from the airport, scorching a wide stretch of the Margalla Hills, including a section behind Faisal Mosque, one of Islamabad’s most prominent landmarks. Twisted metal wreckage hung from trees and lay scattered across the ground.

The cause of the crash was not immediately clear, and rescue workers were seeking the “black box” flight data recorder amid the wreckage. But Defense Minister Chaudhry Ahmed Mukhtar said the government did not suspect terrorism.

Rescue workers and citizen volunteers were hampered by the rain, mud and rugged terrain. The crash was so severe, it would have been nearly impossible for any of the 146 passengers and six crew members to survive, rescue officials said.

“There is nothing left, just piles and bundles of flesh. There are just some belongings, like two or three traveling bags, some checkbooks, and I saw a picture of a young boy. Otherwise everything is burned,” rescue worker Murtaza Khan said.

As the government declared today would be a day of mourning and condolences poured in from the U.S., Britain and other nations, hundreds of people showed up at Islamabad’s largest hospital and the airport seeking information on loved ones.

They swarmed ambulances reaching the hospital, but hopes fell as rescue workers unloaded bags filled with body parts. A large cluster of people also surrounded a passenger list posted near the Airblue counter at the airport.

U.S. Embassy spokesman Richard Snelsire confirmed that at least two American citizens were on board, but he declined to provide any further information on their identities or links to Pakistan.