Greek Prime Minister George Papandreou has vowed to "take any necessary measures" to reduce Greece's deficit.

Papandreou says "the stability program will be implemented in every measure."

His comments came as a strike by civil servants grounded all flights and shut down public services across Greece on Wednesday, as labor unions mounted their first major challenge to the austerity measures.

Air traffic controllers, customs and tax officials, hospital doctors and schoolteachers walked off the job for 24 hours to protest sweeping government spending cuts.

Papandreou was speaking in Paris on Wednesday following a meeting with French President Nicolas Sarkozy. European Union leaders are to discuss Greek's economic woes during a summit Thursday in Brussels.