BEIRUT — Rebel fighters and security forces in Syria clashed near the border with Lebanon and fought over a military barracks in Aleppo on Sunday, while Turkish artillery fired into Syria for a fifth consecutive day in retaliation for cross-border shelling.
On Sunday morning, Syrian forces shelled Tal Abyad, a Syrian border town where rebels recently seized control, according to antigovernment activists.
Around the same time, a Syrian shell landed about 200 yards across the border from Tal Abyad, near the town of Akcakale in Turkey, the Associated Press reported. Akcakale is the town where a Syrian mortar shell killed Turkish civilians Wednesday, prompting the Turkish government to announce a policy of retaliation for every shell that strays across the border.
Turkish forces fired eight shells back into Syria on Sunday. The mounting tensions at the border have raised international concerns that the 18-month-old internal conflict in Syria could draw in neighboring countries or even the NATO alliance, to which Turkey belongs.
It was not clear who fired the shell that landed in Turkey on Sunday, or why. It is not uncommon for mortar and artillery shells to miss their targets by significant margins.
Later Sunday, antigovernment activists reported clashes between rebels and security forces near an artillery position in Tal Abyad.
Fighting across the country on Sunday killed at least 90 people, the AP reported, citing activist groups.
Opposition fighters said they strengthened their hold over the Syrian village off Khirbet al-Jouz, in the northern province of Idlib, which borders Turkey and where violent clashes broke out a day earlier.
The Turkish state-run Anadolu news agency said Sunday that the rebels had regained full control of Khirbet al-Jouz. It said the Syrian army was forced to pull back after an offensive by about 700 rebels.
In Aleppo, the antigovernment Tawhid Brigade said its fighters had penetrated the Hanano military barracks and were fighting government forces inside the compound.
A spokesman for the rebel unit, who uses the pseudonym Abu Mohammed, said that in the fight for the barracks, fighters from his unit were joined by members of Jabhet al-Nusra, an insurgent group that allegedly has ties to Al Qaeda.
Concerns about rebel affiliation with extremist groups have cut both ways in the debate over whether the United States and other countries should offer more direct support to the insurgency.
US officials worry that if more powerful arms are given to the rebels, the weapons will fall into the hands of extremists and be used in terrorist attacks. But some rebels have warned that by denying them the aid they need to win on their own, the West will force the rebels to ally with extremists and their sponsors.
Activists reported fierce shelling near the Aleppo citadel, which dates to the 12th century, and said that about 20 shells fell on the al-Sakur neighborhood of the city in a span of a few minutes.
Intense fighting also broke out Sunday in Syrian villages near the border crossing that leads to the Bekaa Valley in Lebanon, according to Syrian television and antigovernment fighters and activists. Syrian television said security forces battled armed groups that entered the country from Lebanon near the town of Qusayr.
Abdullah, a rebel fighter, said in an interview that Syrian security forces based in the Christian village of Rableh were fighting insurgents based in a nearby Sunni Muslim village, Zira’a.