A Syrian government helicopter on Thursday crashed near the capital Damascus, state-run television said.
Rebels said they had shot down the helicopter in the town of Douma on the outskirts of Damascus, the opposition Syrian Observatory for Human Rights reported.
Rebels also said they had shot down a helicopter in the northern city of Aleppo.
The helicopter was allegedly downed while it was strafing suburban areas of Aleppo near the border with Turkey, according to the rebels.
The government of President Bashar Assad has increasingly been using air power against the rebels.
Aleppo, Syria's biggest city, has been the scene of fierce battles between government troops and rebels for more than two months.
Opposition activists reported fierce battles near Aleppo's military and civil airports.
Elsewhere, fighting was raging between government troops and rebels near the city of al-Rastan in the central province of Homs, a flashpoint in Syria's 19-month conflict, the opposition said.
The latest violence comes after media reports quoting U.S. intelligence documents as saying Iran is using civilian airplanes to transport weapons and personnel to the Syrian government via Iraq under the guise of humanitarian aid.
Want to enjoy 'Zen' reading - with no ads and just the article? Subscribe todaySubscribe now