Turkey has banned all Syrian aircraft from its air space as it takes an increasingly firm stance against President Bashar al-Assad.
Meanwhile, Syrian rebels say they have made more gains in a key province near the Turkish border.
NATO-member Turkey has increasingly taken on a leadership role in the international coalition ranked against Mr Assad.
Turkish confrontation with Syria increased in the past two weeks because of cross-border shelling and escalated on 10 October when Turkish fighter jets forced down a Syrian airliner en route from Moscow.
Turkey said it was carrying Russian munitions for Mr Assad's military.
Russia has said there were no weapons on the plane and that it was carrying a legal shipment of radar equipment.
Turkish Foreign Minister Ahmet Davutoglu said today Turkish air space had been closed to Syrian planes.
Syria banned Turkish planes from flying over its territory last night.
"We made a new decision yesterday and informed Syria. We closed our air space to civilian Syrian flights as well as military flights," Mr Davutoglu said.
The bloodshed inside Syria has worsened markedly in the past two months although neither side has been able to gain a distinct advantage.
Combat has been reported nationwide but the crucial strategic battles are being fought in an arc through western Syria, where most of the population lives.
Rebels surrounded an army garrison on Sunday near a north-western town, in the latest push to seize more territory near the border with Turkey, opposition activists said.
Rebels also posted video on the internet purportedly showing a fighter jet they had shot down in the area the previous day.
Syria accused of dropping cluster bombs in civilian areas
New York-based Human Rights Watch said cluster bombs were dropped from planes and helicopters near the main north-south highway running through Maarat al-Numan, a town rebels seized last week cutting the route from Damascus to Aleppo.
HRW previously reported Syrian use of cluster bombs in July and August, but the renewed strikes indicate the government's determination to regain strategic control in the northwest.
Cluster munitions drop hundreds of bomblets on a wide area, designed to kill as many people as possible. More than 100 nations have banned their use under a convention which became international law in 2010, but Syria has not signed it. Russia, China and the United States have also refused to sign.
Towns targeted included Maarat, Tamanea, Taftanaz and al-Tah. Cluster bombs have also been used in other areas in Homs, Aleppo and Latakia provinces, and near Damascus, HRW said.
"Syria's disregard for its civilian population is all too evident in its air campaign, which now apparently includes dropping these deadly cluster bombs into populated areas," said Steve Goose, arms director at HRW.
HRW said it learned initially about the latest use of the weapons from videos released by opposition activists and had confirmed it in interviews with residents in two towns.
It had no information on casualties. The bombs were Russian-made, but it was not known how or when Syria acquired them, it said.
Syrian government officials were not immediately available to comment on the HRW report.
The official state news agency said today that loyalist forces had killed dozens of "terrorists" in Aleppo, and had captured rockets.