WARSAW -- Ukraine's President Viktor Yushchenko and his Polish counterpart Lech Kaczynski signed a cooperation pact Friday, aiming to improve ties between the two neighbors with a troubled post-World War II history.

Yushchenko was in Warsaw briefly to mark the 60th anniversary of the expulsion of 140,000 Ukrainians, who were ruthlessly removed from their homes in southeastern Poland in 1947 in an attempt by the communist authorities to consolidate control of the region.

"History has left us some not very good pages," Yushchenko said, but added that relations were improving.