PRAGUE — Czech President Vaclav Klaus reluctantly endorsed the European Union’s crucial reform treaty on Tuesday, ending his efforts to block the proposed pact and paving the way for it to finally enter into force.

Klaus, who has been highly skeptical of increasing the EU’s powers, signed the Lisbon Treaty at the Prague Castle at 3 p.m. (1400 GMT), hours after his nation’s Constitutional Court ruled that the document was in line with the country’s constitution.