Polish President Andrzej Duda and his German counterpart gave speeches during the ceremony.

Leaders including German Chancellor Angela Merkel and US Vice President Mike Pence on Sunday mark 80 years since the start of World War Two in Poland, with the conflict still a live political issue in the country.

Few places suffered the level of death and destruction seen in Poland. It lost about a fifth of its population, including the vast majority of its three million Jewish citizens. After the war, shattered Warsaw had to rise again from ruins and Poland remained under Soviet domination until 1989.

Ceremonies begin shortly after 4 am (0200 GMT) in the small town of Wielun, site of one of the first bombings of the war on September 1, 1939, with speeches by Polish President Andrzej Duda and his German counterpart, Frank-Walter Steinmeier.

Ms Merkel, and Mr Pence who is arriving after President Donald Trump abruptly cancelled a planned trip due to a hurricane, will take part in events later in the day in Warsaw.

For Poland's Law and Justice (PiS) party, the memory of World War Two is a central plank of its "historical politics", aiming to counteract what it says is a lack of appreciation in the West of the extent of the nation's suffering and bravery under Nazi German occupation.

Critics say the party's ambition is to fan nationalism among voters at a time when populists around the world are tapping into historical revisionism. PiS says the country's standing on the global stage and national security are at stake.

"The experience of Poland in the Second World War greatly differed from western European countries. The occupation of France and Poland was incomparable," Prime Minister Mateusz Morawiecki wrote in a paid article published by German newspaper Die Welt on Friday.

Paid for by a foundation financed by state companies in Poland, similar articles were due to appear in major newspapers across Europe and in the United States over the weekend.

As part of its campaign, the Polish National Foundation also paid for supplements in some newspapers consisting of a copy of their front pages from Sept. 2, 1939, that highlighted the Nazi German army's attack on Poland.

APPORTIONING BLAME, COST

Wartime remembrance has also become a campaign theme in Poland ahead of a national election due on October 13, with PiS accusing the opposition of failing to protect Poland's image.

"Often, we are faced with substantial ignorance when it comes to historical policy ... or simply ill will," Jaroslaw Sellin, deputy culture minister, told Reuters.

Parallel events are being held in the coastal city of Gdansk, where liberal city authorities have invited left-wing London mayor Sadiq Khan, as well as European Commission deputy chief Frans Timmermans, a long-standing critic of the PiS government.

Under Mr Timmermans, the European Commission has launched legal action against Poland, accusing it of breaching the bloc's rule of law standards.

In a move likely to increase tensions between Poland and Germany, fuelled under the PiS government, Mr Morawiecki renewed calls for wartime reparations in recent days.

Germany, one of Poland's biggest trade partners and a fellow member of the European Union and NATO, says all financial claims linked to World War Two have been settled.

The cancellation of Mr Trump's visit is a disappointment to the PiS government, which is seen as one of Washington's closest allies in Europe. Polish and U.S. officials have said another visit could be scheduled in the near future.

Opinion polls show PiS is likely to win the October ballot. The party's ambition is to galvanise voters and disprove critics by winning a majority that would allow it to change the constitution.