Warsaw - Polish researchers launched a probe on Tuesday into the 1943 death of World War II General Wladyslaw Sikorski, hoping to determine if it was an accident or possible Soviet-planned assassination.

Sikorski's coffin was taken out of its sarcophagus from a crypt in a Krakow cathedral, and was later to be transported for DNA and medical tests. Results are expected in about a month.

Sikorski died on July 1943 while returning from a troop inspection in the Middle East. The Royal Air Force plane crashed into the sea minutes after take-off from Gibraltar.

Sikorski was a Polish leader and statesman who lead the country's government-in-exile during World War II after the Nazi invasion of Poland in 1939.

Soviet leader Joseph Stalin later broke off relations with Poland, citing as a reason Sikorski's request for an investigation into the murder of Polish officers at a forest in Katyn.

The investigation is lead by the Institute of National Remembrance - which examines Nazi and communist crimes in Poland - and is hoped to end 65 years of mystery and conspiracy theories that surround the general's death.

A British report ruled the plane crash as an accident caused by jammed plane controls. But the tense political situation of the time has given rise to a slew of speculation.

By various theories, the assassination was ordered by Stalin, British leader Winston Churchill or even Polish conspirators. (dpa)