Syria said it was ready to work with the United States to fight "terrorism" as US President Barack Obama approved surveillance flights over the nation, a move that could pave the way for air strikes against Islamic militants, two American officials said.
Syria, locked in a civil war with various rebel groups including Islamic State since March 2011, said for the first time on Monday that it would work with the international community, including Washington, to tackle the Islamist problem.
But Foreign Minister Walid Muallem insisted that any strikes on Syrian territory must be coordinated with the government of President Bashar al-Assad.
"Syria is ready for cooperation and coordination at the regional and international level to fight terrorism and implement UN Security Council resolution 2170," Muallem said.
But White House spokesman Josh Earnest rejected the call from Damascus.
"There are no plans to coordinate with the Assad regime as we consider this terror threat," Earnest said. The United States did not even recognise the Assad regime as the legitimate rulers of Syria, he said.
The UN resolution, passed this month, seeks to cut funds and the flow of foreign fighters both to Islamic State and to al-Qaeda's Syrian affiliate, al-Nusra Front.
Western powers fear Islamic State's self-declared "caliphate" could become a launch pad for a new round of global terror attacks.
While the White House says Obama has not approved military action inside Syria, additional intelligence on the militants would likely be necessary before he could take that step. Pentagon officials have been drafting potential options for the president, including air strikes.
The Syrian Observatory for Human Rights said foreign drones were seen over the eastern province of Deir Ezzor on Monday.
One US official said the surveillance flights were an important avenue for obtaining the reliable intelligence the US needed.
The US began launching strikes against Islamic State inside Iraq earlier this month, with Obama citing the threat to American personnel in the country and a humanitarian crisis in the north as his rationale. Top Pentagon officials have said the only way the threat from the militants can be fully eliminated is to go after the group inside neighbouring Syria as well.
Obama has long resisted taking military action in Syria, a step that would plunge the US into a country ravaged by an intractable civil war.
However, his calculus appears to have shifted since Islamic State announced last week that it had murdered American journalist James Foley, who was held hostage in Syria.
The group is also threatening to kill other US citizens being held in Syria.
The White House would not comment on Obama's decision to authorise surveillance flights over Syria.
"We're not going to comment on intelligence or operational issues, but as we've been saying, we'll use all the tools at our disposal," said Caitlin Hayden, spokeswoman for the White House National Security Council.
The two officials who confirmed the decision were not authorised to discuss Obama's decision publicly by name, and insisted on anonymity.
Administration officials have said a concern for Obama in seeking to take out Islamic State inside Syria is the prospect that such a move could unintentionally help the embattled Assad.
UN human rights chief Navi Pillay said abuses by Islamic State and affiliated groups in Iraq against non-Arab ethnic groups and non-Sunni Muslims involved targeted killings, forced conversions, abductions, trafficking, and destruction of holy and cultural sites.
"They are systematically targeting men, women and children based on their ethnic, religious or sectarian affiliation and are ruthlessly carrying out widespread ethnic and religious cleansing in the areas under their control," Pillay said. "Such persecution would amount to crimes against humanity."
Agence France-Presse and Associated Press