Poland's leaders and thousands of people are attending the state funeral of Tadeusz Mazowiecki, Eastern Europe's first post-communist prime minister.

A pro-democracy activist, Mazowiecki served as adviser to the Solidarity freedom movement that ousted Communists from Poland in 1989, and became the first post-communist premier that year. Poland's transformation inspired ouster of communism in the region. He died on Monday at a hospital in Warsaw, aged 86.

European Commission President Jose Manuel Barroso also joined mourners for the funeral Mass at St. John's Arch Cathedral in Warsaw on Sunday. Mazowiecki's simple wooden coffin, covered by Poland's white-and-red national flag was placed in front of the altar that was decorated with yellow roses.

Mazowiecki will be laid to rest in Laski, near Warsaw.