A car bomb exploded in Sayda Zainab, a neighborhood in the Damascus countryside, according to the Syrian Observatory for Human Rights, a London-based opposition group. There was no immediate information on how many people were killed. Saida Zaynab is home to a historic Shia shrine that draws thousands of pilgrims every year.

Fighting between loyalist Syrian forces and fighters from the Free Syrian Army also raged along Syria's border with Turkey, leading Turkish authorities to close schools in the border town of Ceylanpinar.

The Syrian Observatory for Human Rights also said at least 10 rebels and 16 Syrian troops were killed on the Syrian side of the border, in Hasaka province. Some rebels entered Syria from Turkey and engaged the Syrian army in clashes, the group said.

At the same time, Turkish President Abdullah Gul said his country was drawing up contingency plans with the NATO military alliance to fortify its border with Syria.

Gul told reporters Thursday that because of the ongoing civil war in Syria and its possible repercussions for NATO member Turkey, every measure was being considered to counter the risks. Turkish and international media have reported in recent days those options include the installation of Patriot missiles along the border, something Prime Minister Recep Tayyip Erdogan denied Wednesday.

Several stray mortar rounds and a tank shell landed Thursday in the Golan Heights -- captured by the Jewish state from Syria in the 1967 Six-Day War -- as a result of fighting inside Syria, according to the Israeli military.

One of the shells landed in the Israeli settlement of Alonei HaBashan, but there were no reports of damage or injuries, the Israeli military said.