ISTANBUL — For the second time in a week, the civil war in Syria spilled across border areas Wednesday as rebel forces were reported to have driven government troops from a northern frontier crossing in an apparent effort to expand resupply and infiltration routes in the campaign to overthrow President Bashar Assad.
Turkish schools in the region were closed for the day after intense overnight clashes as the rebels attacked the Syrian frontier post at Tal Abyad, south of the Turkish town of Sanliurfa, according to the semiofficial Anatolian News Agency.
Television footage Wednesday appeared to show members of the insurgent Free Syrian Army standing on the roof of the border post and hauling down the Syrian flag at Tal Abyad, less than a mile from Turkey’s Akcakale crossing.
A private Turkish television channel said Syrian tanks were headed for the border post. The attack came two days after Lebanese officials said that Syrian warplanes and helicopters, pursuing opposition fighters, had fired on a Lebanese town near the two countries’ border.
News of the rebel advance came as opposition fighters were forced to withdraw from several neighborhoods in the Damascus suburbs, ceding territory to the army after two weeks of fighting that had forced most residents to flee. Activists said the fighters, shelled for days, withdrew from the al-Hajjar al-Aswad and Qadam neighborhoods, their ammunition exhausted.
Several accounts by human rights groups have asserted that civilians are increasingly caught in combat.
Elsewhere around Damascus, activists circulated footage of what they said was evidence of summary executions by the government in the Jobar neighborhood. In what has become a familiar scene, the video showed at least eight men, all apparently shot in the head, lying in a basement. Another video showed five other dead men with similar head wounds lying in an apartment. The authenticity of the videos could not be independently confirmed.
Several accounts by human rights groups have asserted that civilians are increasingly caught in combat. Amnesty International said Wednesday that Syrian government forces had carried out indiscriminate air attacks and artillery strikes apparently intended to punish civilians perceived as sympathetic to the rebels.
A report by the organization, based on visits to areas of central Syria between Aug. 31 and Sept. 11, said that while much international attention was focused on fighting for Damascus, the capital, and Aleppo, Syria’s largest city and commercial center, ‘‘indiscriminate air bombardments and artillery strikes by the Syrian Army are killing, maiming, and terrorizing the residents of Jabal al-Zawiya and other parts of the Idlib and north Hama regions.’’
“Every day, civilians are killed or injured in their homes, in the street, while running for cover, or trying to shelter from the bombings. Hundreds have been killed or injured in recent weeks, many of them children, in indiscriminate attacks,’’ Amnesty International said.
Iran, one of Syria’s few remaining allies, has made little secret of its aid to Assad’s government. Earlier this week, the head of Iran’s Revolutionary Guard Corps said it had sent personnel to help train members of the Syrian military.
The Iranian assistance is part of an international proxy war in the Syrian conflict. Russia and China also remain supportive of Assad’s government, while Iran’s Persian Gulf rivals, Saudi Arabia and Qatar, have supplied weapons to the rebels, with assistance from Turkey and the United States.
On Wednesday, the Iranian foreign minister, Ali Akbar Salehi, met with Assad in Damascus and briefed the Syrian president on a regional initiative by Egypt, Saudi Arabia, Turkey, and Iran, to halt the fighting, according to Syria’s state news agency. None of the provisions in the initiative call for Assad to step down, a basic demand of the rebel side.
In Turkey, authorities said they completed an inquiry into Syria’s downing of a Turkish warplane in June, concluding it happened in international airspace over the Mediterranean. Syria has asserted the plane was shot down because it violated Syria’s airspace. The shoot-down, which killed the two-man crew, escalated tensions between the neighbors.