Poland and Russia on Saturday mourned thousands of people massacred by the Soviet NKVD secret police during World War Two.

Poland and Russia on Saturday mourned thousands of people massacred by the Soviet NKVD secret police during World War Two and vowed to strengthen the often strained relations between the two neighbors. Polish Premier Jerzy Buzek and Russian Interior Minister Vladimir Rushailo dedicated a cemetery marking the mass grave of some 6,000 Poles shot in pine forests outside the Russian town of Mednoye, 200 km (125 miles) northwest of Moscow. It is one of several mass graves in Russia and Ukraine that hold the bodies of some 22,000 well-educated Poles, including reserve officers, border guards, policemen and civil servants who the Soviets feared would oppose their control of Poland. Soviet troops invaded Poland in September 1939 under a secret pact with Nazi Germany to divide Eastern Europe. The Germans broke the pact in 1941 when they invaded the Soviet Union and the territories it had occupied. In 1943, German troops advancing eastward found the bodies of some 4,000 Polish army officers in a mass grave in Katyn and accused Soviet troops of killing them. The Soviet Union maintained for decades that the Nazis had killed the men during their occupation of the area, admitting responsibility only in the final days of Mikhail Gorbachev's perestroika period. During World War Two, Poland's underground government also searched for officers who disappeared from prisoner of war camps near other towns, including Tver in Russia, from where prisoners were taken to the forest outside Mednoye. The bodies of about 7,000 Poles have never been found.