Smoke rises from buildings after what activists said was shelling from forces loyal to Syria's President Bashar al-Assad in the besieged area of Homs on Jan. 15. (STRINGER/REUTERS)

A top Syrian government official said Wednesday that Western intelligence officials have visited Damascus to solicit cooperation against militants linked to al-Qaeda, a claim that appeared intended to buttress the regime’s attempts to win back international support in the name of fighting terrorism.

The assertion came as the fighters with the Islamic State of Iraq and Syria (ISIS) retook control of many areas in Syria that the group had lost to more-moderate rebels this month, dashing hopes of the Syrian opposition that the extremists’ influence could be quelled ahead of crucial peace talks in Switzerland next week.

Syrian President Bashar al-Assad has clearly signaled that he regards the peace conference as the launch of an international counterterrorism effort rather than an attempt to negotiate peace terms with his opponents, who have not said whether they will attend.

On Wednesday, European diplomats confirmed that visits by intelligence officials to Damascus had taken place but said they were intended only to seek information about kidnapped citizens and extremist fighters.

In an interview that aired on the BBC on Wednesday, Deputy Foreign Minister Faisal Miqdad implied, however, that the agents were seeking broader cooperation with the Syrian government against the threat of militants linked to al-Qaeda who have shot to prominence across rebel-held territory in northern Syria over the past year.

Although most Western countries have called on Assad to hand over power, “there is a schism between the political and security leaderships of these countries,” he said. “Many of these countries have contacted us to coordinate security efforts.”

In Washington, the State Department described as “preposterous” the notion that Assad could be regarded as an ally in the war on terrorism and denied that the United States had been part of any intelligence outreach to the Syrian government.

“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,” said spokeswoman Marie Harf. “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 reported Tuesday that the countries whose intelligence officials have consulted with Damascus include Spain, Britain, France and Germany and that the contacts were primarily aimed at securing information on the hundreds of European citizens who have volunteered to fight alongside Syrian rebel groups.

Diplomats in Beirut said the visits had been arranged to seek information about missing citizens.

“This is not a realignment; it is about ongoing kidnap cases,” said one diplomat who spoke on the condition of anonymity because of the sensitivity of the subject.

Dozens of Westerners, including at least two Americans — journalists Austin Tice and James Foley — are missing in Syria. Most are believed to be held by militant groups, although the State Department has said it suspects that the government detained Tice, who was a freelance contributor to The Washington Post.

While Harf denied that U.S. intelligence officials had visited Damascus, she said she did not know whether there have been other U.S. contacts with the Assad regime. The United States and most European nations ended or shrank their diplomatic presence in Damascus in 2012 because of deteriorating security conditions, but none severed ties, and many European countries regularly send diplomats to the Syrian capital for brief fact-finding trips.

In a sign that many of Assad’s foes also oppose the presence of the most extreme militants, a range of moderate and Islamist rebel units rose up this month to drive ISIS from many parts of rebel-controlled northern Syria.

After seemingly being caught off guard by the challenge, ISIS fighters have since reasserted control over their main strongholds, leaving them more powerful than they previously were in some places.

The ISIS fighters had spread themselves thinly across many parts of the provinces of Aleppo and Idlib, where they shared power with other rebel groups, and they have now been expelled from some of their bases, said Aymenn al-Tamimi, who monitors jihadist activity with the Middle East Forum.

At the same time, they have asserted full control over the eastern provincial capital of Raqqah, captured the important border town of Tal Abiyad and restored their dominance over a number of towns in Aleppo province.

“It does seem the gains have outweighed the losses,” Tamimi said. “Now that they have much fewer localities to defend, they are holding onto them quite tenaciously.”

Ahmed Ramadan contributed to this report.