ISLAMABAD -- Emergency teams battled heavy rains and mud Thursday to recover bodies strewn over hills overlooking the Pakistani capital following the country's worst-ever plane crash.

Authorities speculated that monsoon weather the day before may have been a factor in the crash of the Airblue flight from Karachi to Islamabad. The plane was apparently off course when it slammed into the Margalla Hills, killing all 152 people on board.

Army troops and civilian rescue workers searched a large stretch of the hills scorched by the crash, but tough conditions slowed the pace of operations, said Ramzan Khalid, spokesman for the Capital Development Authority, which helps deal with emergencies. Helicopters could not fly in the heavy rain, he said.

Dozens of relatives and friends of those killed slept outside Islamabad's largest hospital overnight, hoping to receive the bodies of their loved ones. They were still there Thursday morning, hugging one another as their tears mixed with the heavy rain, but only a few were able to retrieve their relatives' corpses.

The plane's "black box" flight data recorders have yet to be recovered. Information extracted from them will be key in determining the cause of the crash. Defense Minister Chaudhry Ahmed Mukhtar and other officials have said the government does not suspect terrorism.

Even when the search is completed, it could take days to identify all the victims with DNA testing since most of the bodies were torn apart and burned in the crash, a grim scene described by rescue workers scouring the twisted metal wreckage.

"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.

The crash was the latest tragedy to jolt a country that has seen thousands of deaths in recent years from al-Qaida and Taliban attacks.

The U.S. Embassy said at least two American citizens were on the plane, an Airbus A321, which was carrying 146 passengers and six crew members.

In the U.S., Paulette Kirksey said that her godmother, Rosie Ahmed of Gadsden, Alabama, and her husband, Saleem Ahmed, were among those on the plane. Rosie Ahmed was in Pakistan to arrange for her husband to move to the United States, Kirksey said. She said Rosie Ahmed was in her late 50s.

The Pakistani government declared Thursday a day of mourning for those lost in the crash.

As of Wednesday night, when rescue work was suspended till the morning, 115 bodies had been recovered, federal Information Minister Qamar Zaman Kaira said.

The control tower at Islamabad airport lost contact with the plane as it was trying to land Wednesday morning, said Pervez George, a civil aviation official. Several officials noted the plane seemed to be an unusual distance from the airport, which was some nine miles away.

Raheel Ahmed, a spokesman for the airline, said the plane had no known technical issues, and the pilots did not send any emergency signals. Airbus said it would provide technical assistance to the crash investigators.