Western intelligence officials visited Syria to discuss security cooperation with the regime against Islamist extremists among the Syrian opposition, a senior Damascus official claimed to the BBC.
US officials denied the report, which comes amid mounting concern in Western capitals about Syria's civil war drawing in foreign radical fighters who may return to carry out attacks in the homelands.
Syrian Deputy Foreign Minister Faisal Mekdad told the BBC the alleged visits to Damascus pointed to a "schism" between what Western politicians say about President Bashar al-Assad's regime and what Western security services do in practice.
Separately, the Wall Street Journal newspaper reported that British, German, French and Spanish agencies have been speaking to Assad regime officials since mid-2013.
Western governments have backed the opposition fighting to topple Assad but are increasingly concerned about the influence jihadist groups are wielding in Syria's nearly three-year-old civil war.
They are also worried about fighters from their countries travelling to Syria to join Islamist militants.
Mekdad said Western agencies were asking for security cooperation.
"I would not specify but many of them have visited Damascus, yes," Mekdad said in a broadcast aired Tuesday night.
"When these countries ask for security cooperation, then it seems to me there is a schism between the political and security leadership.
"Many of these countries have contacted us to coordinate security measures."
Last month the United States and Britain suspended their non-lethal aid to the opposition, fearing the growing influence of radical Islamists in the conflict.
Britain's Foreign Office refused to comment on what Mekdad said, saying it does not comment on intelligence matters.
Citing informed sources, the BBC said the US, British and German intelligence agencies were among those which had sent officials to Damascus.
But State Department deputy spokeswoman Marie Harf denied there was any involvement by US intelligence agencies in talks on counterterrorism.
"This specific report about intelligence agenices going to work with the Assad regime on counterterrorism... is not true," she told reporters.
"We clearly consider the terrorist threat inside Syria to be of serious concern, but it's absurd to consider Assad or the regime a partner in countering that threat," she added.
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"It is because of the climate they have created in the country... that terrorists are able to operate so freely in Syria today."
The Wall Street Journal, citing diplomats and officials, said a retired officer from Britain's MI6 foreign intelligence agency was the first to visit, in the middle of 2013.
German, French and Spanish agencies have been speaking to regime officials since November, the US daily said.
The newspaper said the talks were narrowly focused on extremists and on Al-Qaeda's growing strength in Syria and did not represent a broader diplomatic opening.
AFP reported in November that Western intelligence services had been making contact with Syrian counterparts to test old ties.
Britain and France sent agents to meet the powerful Syrian secret service chief, General Ali Mamluk, whose name figures on a European Union blacklist banning contact.
They were told Syria was ready to resume cooperation but not while the countries' embassies remain closed, sources said.
French President Francois Hollande said Tuesday that 700 people had left France to join the fighting in Syria.
And British Foreign Secretary William Hague said on Monday that hundreds of Britons had also gone to Syria to fight.
This has raised fears that foreign veterans of the conflict could pose a heightened security threat at home upon return.
Shiraz Maher, a senior research fellow at the International Centre for the Study of Radicalisation at King's College London university, said they estimate that between 200 and 366 British nationals have gone to Syria to participate in the conflict.
"We do think it's a growing problem," he told BBC radio on Wednesday.
But he said the "overwhelming majority" of foreign jihadists in Syria "express no desire to return".
"Indeed, a number of those we have been speaking to have died," he said.
The centre estimates that only 30 to 50 fighters have returned to Britain.
He said it was "fairly obvious to be able to identify networks of people who are going over to Turkey in the first instance before crossing the border".