Ceremonies have been held in Poland to mark the start of World War II 70 years ago.
The leaders of more than 20 nations from both sides - including German Chancellor Angela Merkel and Russian Prime Minister Vladimir Putin - are attending.
The BBC reports the day began at the exact time and location where a German battleship fired at a Polish fort on Westerplatte peninsula on 1 September 1939 - the first shots of World War II.
Eastern Poland was occupied by Soviet forces on 17 September.
Earlier in Gdansk, Polish President Lech Kaczynski described the Soviet invasion as "a stab in the back".
Germany and Russia signed a secret deal in Moscow on 23 August 1939.
The Molotov-Ribbentrop Pact led to the carve-up of Poland between Nazi Germany and the USSR, as well as the annexation by the USSR of eastern Finland, Estonia, Latvia, Lithuania and northern Romania.
Western parts of Ukraine and Belarus, formerly Polish territory, were also incorporated into the Soviet Union.
Mr Kaczynski also recalled the Katyn massacre of 1940, in which 20,000 Polish officers were killed by Soviet secret services, saying it was an act of chauvinism and in revenge for Polish independence.
Ms Merkel said: "No country suffered from German occupation as much as Poland."
Mr Putin said all pacts with the Nazis were "morally unacceptable".
An estimated 60 million people lost their lives during the war.