Syria's foreign minister said U.S.-led air strikes had failed to weaken Islamic State it in Syria and the jihadist group would not be tackled unless Turkey was forced to tighten border controls.
A U.S.-led alliance started attacking Islamic State targets in Syria in September as part of a wider effort to destroy the al Qaeda offshoot that has seized large areas of the country and neighboring Iraq.
"All the indications say that (Islamic State) today, after two months of coalition air strikes, is not weaker," Foreign Minister Walid al-Moualem said in an interview with the Beirut-based Al Mayadeen TV broadcast on Friday.
The Syrian government has said it was willing to join the fight against Islamic State, but the United States refuses to deal with President Bashar al-Assad, who it says has lost legitimacy and must leave power.
"If the Security Council and Washington do not force Turkey to control its borders then all of this action will not eliminate (Islamic State)," Moualem said, referring to foreign jihadists who have crossed into Syria from Turkey.
Turkey, which has a 900 km (560-mile) frontier with Syria, has strongly denied accusations it has supported militant Islamists, inadvertently or otherwise, in its enthusiasm to help Syrian rebels topple Assad.
Thousands of foreign fighters are believed to have joined the Islamist militants in their self-proclaimed caliphate, carved out of eastern Syria and western Iraq.
Moualem said Turkish calls for the establishment of a no-fly zone in northern Syria would lead to the partition of the country, adding that Turkey had designs on Syrian territory.
Turkey has repeatedly said a no-fly zone should be put in place to create safe areas in Syria, allowing Syrian refugees in Turkey to be repatriated. Turkey's idea has received a cool reception from its allies. A top NATO general said this week the idea was not being considered.
Moualem held talks with Russian President Vladimir Putin and Foreign Minister Sergei Lavrov on the Black Sea as part of a renewed Russian diplomatic push to restart peace talks on Syria.
The effort is unlikely to get far because Russia rejects calls by Assad's Syrian, Western and Arab opponents for his swift departure. "After our discussions with the Russian side we agreed that the dialogue will be with the national opposition that is not linked to the outside," Moualem said.