Polish rescue workers have pulled another victim from the wreckage of a head-on collision between two passenger trains, raising the death toll to 16. Officials say they believe they have found all the victims of the crash.

Rescuers worked all night Sunday to look for survivors and recover bodies. Saturday's crash injured at least 56 people, some seriously. While most of the victims were Polish, an American woman was among the dead, while citizens of Ukraine, Moldova and the Czech Republic were injured.

The impact left tons of mangled metal on the tracks, with train cars overturned and piled on top of each other.

Prime Minister Donald Tusk visited the crash site Sunday, calling it “the most tragic train catastrophe” in Poland in recent years. President Bronislaw Komorowski announced two days of national mourning.

A White House spokesman says U.S. President Barack Obama sent his deepest condolences to the victims' families and that the United States is ready to send whatever help is needed.

Authorities say the trains were traveling toward each other on the same track when they crashed in Szczekociny in southern Poland. One train was headed to Warsaw, from the southeastern city of Przemysl, while the other was heading south from Warsaw to Krakow.

Officials are investigating to determine how one of the trains ended up on the wrong track.