German Foreign Minister Guido Westerwelle warned today against undermining Europe's liberalised travel policies with reforms to the passport-free Schengen area.

After a joint Franco-Italian letter to the European Commission asking for the possibility of restoring border checks in exceptional circumstances, Westerwelle said travel freedom was one of the continent's cherished policies.

"If you can improve the Schengen system then that is good and you should," Westerwelle told reporters.

"But travel freedom in Europe is such an important achievement that it should not be up for renegotiation."

Tens of thousands of mainly Tunisians have fled democratic uprisings and crackdowns in north Africa since January, most heading for Europe through Italian shores including the tiny Mediterranean island of Lampedusa.

The commission said Tuesday it was drawing up "precise conditions" under which states unhappy with the realities of borderless travel across the Schengen area may temporarily police internal frontiers once more.

However officials stressed there would be no return to routine border controls within Europe.

Italy has accused EU partners of abandoning it in the fight against economic immigration.

Paris in turn has accused Rome of abusing Schengen by issuing temporary residence permits and travel documents to migrants in the knowledge many among the French-speaking Tunisians want to go to France.

The joint letter by French President Nicolas Sarkozy and Italian Prime Minister Silvio Berlusconi was aimed at cooling the row between the neighbour states.