Russia's Orthodox Church and Poland's Roman Catholic Church pledged on Thursday to help their nations overcome a painful shared past and move towards reconciliation.
The two churches, very influential in their own countries, agreed at a rare meeting of senior clergy to draw up a joint document that will express their Christian vision of how the two Slavic neighbours can come together.
"The idea is to look at the history of our nations from our Churches' point of view. During the history of our nations we have experienced glorious moments but also very painful ones," Stanislaw Budzik, a Polish bishop, told a news conference.
"As Christians we should reflect on the history of our nations and call for mutual love and cooperation," said Budzik, general secretary of the Polish Bishops' Conference.
Conflicts between Russia and Poland stretch back centuries.
Soviet Russia joined Nazi Germany in 1939 in carving up Poland and Josef Stalin ordered the murder of 20,000 Polish officers in 1940 in Katyn forest.
After World War Two, Moscow imposed an atheistic communist regime in Poland that lasted until 1989.
The churches' initiative coincides with a cautious rapprochement between the governments that has gathered pace since a plane crash in Russia in April killed Poland's President Lech Kaczynski, triggering an outpouring of Russian solidarity.
Kaczynski and his 95-strong entourage had been heading to Katyn to mark the 70th anniversary of the massacre there.
Russia and Poland remain at loggerheads over a host of issues including NATO expansion and missile defence, but want to focus more on their burgeoning trade relations.
Archbishop Hilarion Alfeyev, head of the Russian Orthodox Church's external relations department, said the churches would steer clear of politics in their document, which he said would probably take up to a year to complete.
"Our aim is to call for mutual forgiveness and reconciliation so the errors of the past are not repeated in the future. Our aim is to seek those things common to us both... such as Christian history," he said.
The Catholic and Orthodox Churches have been split since the Great Schism of 1054 and relations have often been poor, but Russia's Patriarch Kirill has assigned a high priority to improving inter-faith dialogue since his election last year.
A historic meeting between Kirill and German-born Pope Benedict is now in prospect. SIC: KP