Klaus, a staunch Eurosceptic, announced he had signed the Lisbon Treaty at Prague Castle, just a few hours after the Czech Constitutional Court ruled that the treaty is compatible with the country's constitution.
An hour later, he held a televised press conference during which he said he had expected the verdict to be in favour of the Lisbon Treaty. He said he respected the ruling but he does not agree with it.
"The treaty's enforcement will limit the Czech Republic's sovereignty, regardless of the Constitutional Court's verdict," he added, quoted by the Czech press.
Klaus lashed at the court's judges, describing their behaviour as "obstructive" and their verdict as "politically motivated".
According to EU practice, new treaties enter into force on the first day of the month after they are deposited in Rome. This means that the Lisbon Treaty could enter into force at on 1 December, with a new 27-member European Commission, a permanent Council president and a High Representative for Foreign Affairs being selected in the meantime.
Joseph Daul, Chairman of the EPP group, welcomed the news from Prague. "Europe can now move forward. The conclusion of the ratification process means that the treaty will enter into force without further delay this year. The treaty will allow effective European action in areas where solutions are urgent, such as the financial and economic crises, climate change and energy," he said.
"I call on the European Council to nominate the College of the European Commission, the High Representative for Foreign Affairs and Security Policy and the president of the Council without delay," Daul further declared.
The Swedish EU Presidency is widely expected to call an extraordinary EU summit to decide on the top jobs, most likely to be held on 13-14 November.
It took eight years of intricate negotiations for the EU's new reform treaty to see the light of day, since EU leaders first debated its proposed reforms at the 14-15 December Laeken summit in 2001.