WARSAW, Sept. 1 (Xinhua) -- "We are obliged to make an appeal once more: no more war", Polish Prime Minister, Mateusz Morawiecki wrote in a letter read on Saturday in Wielun, central Poland, where the events commemorating 79th anniversary of World War II outbreak were held.

"We must send a message that we will continue to make an effort to build peace, again and again. In a place sanctified by the blood of the innocent, we are obliged to make an appeal once more: no more war", Morawiecki wrote.

During the ceremony in Wielun, also the memorial roll-call was read. In the presence of state and local government authorities, an honorary salvo was made and flowers were laid at the monument to commemorate the victims.

At the same day, ceremonies were also held at Westerplatte, northern Poland, at the site of the first clash between Polish and German forces in September 1939. The observances commenced at 4:45 a.m.local time with the presence of the prime minister, Speakers of lower and upper house of the Polish Parliament and government representatives.

In his speech, Morawiecki called on Westerplatte to become a place of concord. At the end of ceremony, delegations of authorities as well as war veterans laid flowers and lit candles at Monument to the Defenders of the Coast.

Wielun and Westerplatte peninsula were two first sites under attack. Wielun was a city bombarded by the Nazi Germany on Sept. 1, 1939, with almost 1,200 civilian victims.