UNITED NATIONS - The United Nations on Tuesday condemned fighting by Syrian forces close to a Golan Heights ceasefire line with Israel as a new threat to stability in the region.

Israel demanded action by the UN Security Council after one of its patrols in the buffer zone was hit Monday by bullets fired by Syrian forces who are battling rebels in the area.

UN spokesman Martin Nesirky said a mortar shell and a tank round fired from the Syrian side of a ceasefire line created in the Golan Heights in 1974 had landed on Israel's side.

"The presence of military personnel and the military operations in the area of separation are grave violations of the 1974 agreement" setting up the demilitarized zone, Nesirky said.

"It has the potential to escalate tensions between Israel and Syria and jeopardizes the ceasefire between the two countries and the stability of the region," the spokesman added, highlighting the "serious safety and security risks" to the UN unarmed force in the Golan.

The UN's top political official Jeffrey Feltman said the fighting in Golan and increased tensions in Lebanon and Turkey showed that the "risk is growing that this crisis could explode outward into an already volatile region."

Syria, stricken by a 20 month old uprising against President Bashar al-Assad, remains formally at war with Israel, which captured part of the Golan Heights in a 1967 war and annexed it in 1981. The move has never been recognized by the international community.

Since a 1974 agreement between the two countries, a 1,200-strong unarmed UN force, UNDOF, has patrolled the Golan buffer zone.

Nesirky said UNDOF had seen Syrian forces "conducting operations with at least four main battle tanks and mortar fire inside the area of separation."

He said the Golan was "relatively quiet" on Tuesday but the UNDOF commander was trying "to prevent an escalation of tension" between Syria and Israel.

Israeli diplomats said the Syrian tanks appeared to have left the buffer zone but there was still fighting between the Syrian army and rebel groups as part of the 20-month old uprising against President Bashar al-Assad.

The Israeli military patrol was hit by gunfire from the Syrian side on Monday. Israel's UN ambassador Ron Prosor said his country viewed the heightened tensions with "utmost concern."

Prosor also called the presence of Syrian tanks in the Golan buffer zone a "grave violation" of the 1974 agreement zone.

"This represents a dangerous escalation that could have far-reaching implications for the security and stability of our region," Prosor said in a letter to the Security Council.

"Israel has shown maximum restraint. However, Israel views the continued violations of the Separation of Forces agreement by the Syrian military forces with the utmost concern," the ambassador added.

"The international community and the Security Council should address this alarming development without delay to prevent further escalation," Prosor said.

A military spokesman said an Israeli vehicle was hit by stray bullets on Monday while it was near the Golan ceasefire line. There were no injuries.

Israel's armed forces chief, Lieutenant General Benny Gantz, said Sunday his country could become involved in the Syrian conflict, as fighting between the army and rebels raged near Israeli positions on the strategic heights.