Some western nations opposed to President Bashar al-Assad have discussed security co-operation with his government, Syria said on Wednesday, a move which if true would suggest a rise in western concerns about foreign militants in rebel ranks.

The UK government denied having any such co-operation with the Assad regime and the top US and French diplomats both said they were personally unaware of such contacts though did not go so far as to deny that any had taken place.

Syria's deputy foreign minister Faisal Mekdad said several western intelligence services had visited Damascus for discussions. His comments were broadcast a day after the Wall Street Journal reported that French and Spanish spy services had made contact with Assad's government. French media have carried similar reports.

"I will not specify [which countries] but many of them have visited Damascus, yes," Mekdad said in a BBC interview.

Any suggestion that western countries were talking to Assad's government could complicate their relationships with opposition groups supported by the United States and Europe, and with wealthy Gulf states that fund the rebels.

Asked about the report, US secretary of state John Kerry indicated he was not aware of such contacts.

"I don't know anything about that, certainly not under my auspices," he told reporters in Kuwait, where he is on a visit.

In Paris, French foreign minister Laurent Fabius declined to comment, although when pressed he said he had the "same position" as Kerry. The defence ministry declined to comment.

The French newspaper Le Figaro reported in December that the DGSE external intelligence service had gone to Damascus to discuss cooperation on terrorists. Damascus had replied that it would do so if France re-opened its embassy, it reported.

There was no immediate reaction from officials in Germany or Spain.

Western powers have long supported Syria's opposition with rhetoric but the past year has seen a shift in emphasis, with countries backing away from material aid to the rebels as al-Qaida-linked groups have gained power in rebel-held regions.

Western countries are worried about the presence in rebel ranks of foreign Islamist militants who have travelled to Syria to join a near three-year-old struggle to topple Assad.

"Frankly speaking the spirit has changed," Mekdad said. "Many of these countries have contacted us to coordinate security measures."

"When these countries ask us for security cooperation, then it seems to me there is a schism between the political and security leaderships," he added.

Assad has always maintained that the uprising against him is run by terrorists and that western support for the rebels damages western countries' own interests.