Thousands of passengers, many of whom Christmas travelers, are stranded at airports around Europe as snow, ice, fog and low temperatures continue to disrupt the air traffic.

The way the European airport operators have handled the inclement weather conditions has led to criticism by the European Commission, with one of the most troubled airports, London's Heathrow, where many passengers including Bulgarians, have been stranded for as much as 4 days, resisting offers to send in the UK army to help, the BBC reported.

Dozens of airports in the UK, Germany, France and Ireland are experiencing trouble because of the weather, with Eurocontrol, the European air traffic watchdog announcing that some 3000 flights have been canceled in the past four days.

British Airways said that in line with a directive from BAA, it would operate only a third of its normal flight schedule at Heathrow until 6 am GMT on Thursday. In Ireland, the Dublin Airport Authority said the airport would be closed until at least 08 am GMT on Wednesday, the The Irish Times reports, as cited by the BBC.

Germany's Frankfurt Airport canceled 550 of almost 1 300 flights on Tuesday because of the bad weather.

Many passengers sought to travel by rail instead of plane, causing Eurostar to recommend that passengers trying to leave from London should cancel their tickets and stay at home.

The European Commission said it was "extremely concerned" about the level of disruption caused by the severe snow, saying that it was "unacceptable and should not happen again".

According to data from Airports Council International (ACI), the professional association of European airport operators, 88% of flights to and from European airports had been operating.

UK Prime Minister David Cameron said he was "frustrated" it was taking so long to get Heathrow fully operational again.