WARSAW: Poland's President Lech Kaczynski signed the European Union's reforming Lisbon Treaty in a ceremony Saturday, leaving his ultra-eurosceptic Czech counterpart Vaclav Klaus as the only holdout.

"The fact that the Irish people changed their minds meant the revival of the treaty, and there are no longer any obstacles to its ratification," Kaczynski said before inking the text.

"Today is a very important day in the history of Poland and the European Union," he added, as senior EU leaders looked on.

Among them were European Commission president Jose Manuel Barroso, European Parliament speaker Jerzy Buzek, who is Polish, and Swedish Prime Minister Fredrik Reinfeldt, whose country currently holds the EU's rotating presidency.

"President Kaczynski has set the seal on the very important chapter for Poland and for the European Union," Barroso said.

The ceremony took a light-hearted turn when Kaczynski's fountain pen appeared to run out as he began signing and the smiling president asked an aide for a replacement.

The treaty aims to streamline the running of the EU, which has nearly doubled in size in the past five years as a swathe of ex-communist countries such as Poland have joined.

The text -- which notably creates a new full-time president and foreign minister for the EU -- has to be approved by all 27 member states in order to come into force.

Polish lawmakers ratified it in April 2008, but the eurosceptic Kaczynski refused to complete the process in the wake of Irish voters' rejection of the text in a referendum that June.

Kaczynski repeatedly said that Poland did not want to block the treaty as such, but that he would wait until the Irish approved it, which they did on October 2 in a second referendum.

He had argued that the EU's big member states should not lay down the law for small countries like Ireland. Poland has a population of 38 million, placing it among the bloc's heavyweights.

"Today, the signature of President Kaczynski brings us one step closer... However, the Czech Republic still needs to complete the steps, with the signature by President Klaus," Reinfeldt said.

"Europe eagerly awaits this happening. We do not need more delays," he added.

Klaus, a staunch eurosceptic who refuses to fly the EU flag at his residence, has repeatedly refused to sign the treaty, and on Friday imposed a new condition, seeking an opt-out on a key element, the Charter of Fundamental Rights.

Klaus warned that otherwise the treaty would "worsen the position of our country and expose it to new risks".

He raised the spectre of the charter enabling the European Court of Justice unpicking Prague's post-war decrees on the seizure the property of ethnic Germans and Hungarians and their expulsion from the then Czechoslovakia on the grounds that they had collaborated with the occupying Nazis during World War II.

He pointed to Poland and Britain, which obtained exemptions: Catholic Poland was assured the charter would not force it to allow gay marriage, and Britain that European laws and courts would not prevail over its own judicial system.

Even if his condition is met rapidly, Klaus would not be able to sign the treaty at once, since his country's top court banned him from ratification while it considers a plea from eurosceptic members of parliament that it may be unconstitutional.

The verdict of the Constitutional Court is expected to take at least two weeks.