Russian search teams continue recovering bodies and pieces of wreckage at the site where a Russian airliner crashed in the Black Sea on Thursday, killing up to 78 people on board. Investigators are also trying to determine just what caused the plane to explode, as it flew from Tel Aviv to Siberia.

The grim task of recovering the remains of those killed in the crash continues off the Russian coast in the Black Sea. Search teams have also found many large pieces of wreckage, which investigators hope will solve the mystery of what caused the plane to explode.

One of the ships at the scene has specialized equipment that can scour the sea floor to search for the plane's flight data and voice recorders.

Russian officials say the disaster could have been an act of terror, or some sort of mechanical malfunction. But the most prevalent explanation is that a Ukrainian missile accidentally hit the plane and caused it to explode.

Ukraine was test-firing missiles on the nearby Crimean peninsula at the time, and on Friday, Ukraine's prime minister said the missile theory was possible. His comment came after Ukrainian military officials strongly denied that a missile was to blame. They said the plane was flying well outside the range of the test exercises.

On Thursday, Russian President Vladimir Putin appeared to accept that explanation. Russia's defense minister has asked the U.S. military to provide evidence that the Pentagon says shows a missile might have hit the plane.

Soon after the crash, Pentagon officials said a satellite had detected a missile's plume of smoke in the area where the plane was passing. Most of the passengers on board were Israeli citizens of Russian origin, who were traveling to the city of Novosibirsk, in Siberia. Some relatives of the victims have arrived in the southern Russian city of Sochi to help identify remains.