Poland is holding day-long ceremonies honoring late President Lech Kaczynski and the 95 others who were killed in a 2010 plane crash in Russia, amid revived allegations that the crash was a conspiracy by Russia and Poland's government at the time.

The allegations come from the ruling Law and Justice party led by the late president's twin.

Jaroslaw Kaczynski and his followers claim they have evidence that "almost certainly" proves that the president's plane was attacked as it was preparing to land.

Official investigations by Poland and Russia have concluded that the crash was an accident caused by errors of the crew trying to land in heavy fog.

On Sunday, Jaroslaw Kaczynski and government officials were taking part in prayers and wreaths' laying at the victims' graves and memorials.