Airlines must scrupulously honour the rights of air passengers stranded abroad by the flight chaos created by a volcanic ash cloud over Europe, the EU Commission insisted Wednesday.

Transport Commissioner Siim Kallas is "very, very concerned about the reports he hears" of travellers facing problems getting full reimbursement of cancelled flight tickets or receiving proper care and help in terms of food and drink and accommodation, his spokeswoman Helen Kearns told reporters.

Her comments came as Europe's skies began to resume something close to normal operations for the first time in almost a week, with some three-quarters of scheduled flights expected to go ahead.

However hundreds of thousands of passengers remain stranded after being unable to return home from holidays, family visits or business trips.

Nearly seven million passengers have been affected by the blanket shutdowns, which governments have insisted were essential on safety grounds, given the possibility that the ash could choke up jet engines and provoke air disasters.

European passengers "have some of the tightest rights in the world to protect them," said Kearns, when questioned on horror stories of passengers forced to waive some rights if they wanted to get on flight lists or not receiving full compensation for wasted tickets and ancillary expenses.

"The message to national enforcers and the message to the public is that European passenger rights apply in difficult circumstances as in a normal situation," she underlined.

According to European law, EU passengers have the right to full reimboursement of airline tickets, including taxes, or for the carrier to arrange alternative measures to get them to their destination.

If this latter approach is taken then hotel rooms and sustenance have to be provided until those alternative arrangements take place.

The European Commission offers its free Europe Direct telephone information service to European consumers with more queries. The number, which can be reached from anywhere within the European Union, is: 0800 6789 1011.