WARSAW -- Polish President Aleksander Kwasniewski signed his country's European Union accession treaty on Wednesday, completing the EU's biggest future member's formalities for entering the bloc on May 1, 2004.

Kwasniewski signed the treaty in the same room in the presidential palace where the Soviet-led Warsaw Pact was founded in 1955, one and a half months after Poles said a big ‘Yes’ to joining the EU in a referendum.

"Who would have imagined that one day, in this room, this same room in which on May 14 1955 the Warsaw Pact was created, nearly 50 years later, we would witness Poland's return to an undivided Europe," Kwasniewski said.

Signing the treaty in the presence of Prime Minister Leszek Miller, Foreign Minister Wlodzimierz Cimoszewicz and many other guests, Kwasniewski called for a nation-wide mobilization by Polish institutions to prepare for membership, stressing that entry "implies not only rights but also duties".

"I am convinced that we are capable of such an effort," he said.

The ceremony opened with the Polish national anthem and ended with Beethoven's Ode to Joy, which has turned into the expanding EU's anthem, AFP reported.

At a June 7-8 referendum Polish voters agreed by 77.45 percent to 22.55 percent to join the EU. The turnout was 58.85 percent.

Poland is the biggest of 10 countries on course to join the EU. Only Estonia and Latvia, two Baltic former Soviet republics, still have to hold referendums on September 14 and 20 respectively.