Leaders of the two countries, meeting for a summit in Spain on Tuesday, agreed to start inspecting vessels deemed dangerous, and if appropriate, to force them out of the 320km economic exclusion zone around their coastlines.

"We have decided that as of Wednesday all the vessels of a dubious character will be liable to be inspected and, if need be, excluded from our 320km zones," said French President Jacques Chirac.

A French submarine has begun its voyage to the site where the Prestige tanker sank in the Atlantic last week, to check whether it is still leaking oil.

The three-man Nautili left Nice on Tuesday evening and is heading for the tanker's resting place, where it is expected to arrive on Sunday.