Syrian army forces crossed the demilitarized zone near the border with Israel in the Golan Heights last week, a highly unusual incident, on what is considered a quiet border.

Following the incident, in which 500 soldiers and 50 vehicles crossed into the demilitarized zone, Israel filed a formal complaint to the UN secretary general and to the president of the UN's Security Council, warning that the event may have serious ramifications.

Concern in Israel, in light of the situation in Syria, especially over Assad's chemical weapons stockpile and land-to-land missiles, is growing every day. In a meeting on Sunday afternoon, Prime Minister Benjamin Netanyahu consulted the heads of Israel's security establishment, including Defense Minister Ehud Barak, Foreign Minister Avigdor Lieberman and other senior cabinet members.

"We are monitoring the events in Syria closely and are prepared for any development to come," Netanyahu said in his opening statement.

The Syrian soldiers entered the demilitarized zone last Thursday. The Syrian forces entered the area near the Syrian village of Jubata Al Khashab, a few kilometers east of the Israeli Druze village of Mas'ada in the northern part of the Golan Heights. It seems that the soldiers' entrance to the demilitarized zone was a result of the fighting with the rebel army.

On the same day, Barak was touring the border with Syria and observed clashes on the other side of the border. Barak, noting that the battle was being conducted at a distance of only "200 meters from UN forces and some 800 meters from the border fence," was not aware at the time that the Syrian soldiers had entered the demilitarized zone.

The demilitarized zone in the Golan Heights is defined in the separation of forces agreement signed by Israel and Syria in 1974. The accord defined a 3-6 kilometer zone which would be demilitarized by Israeli and Syrian forces, and would be under the supervision of a UN military force and Syrian civilian authority. The UN peacekeeping force – UNDOF – includes some 1,000 soldiers, sent from Canada, Poland, Finland and Austria, who are monitoring the keeping of the agreement.

A source within the Foreign Ministry says Israel's view of the Syrian violation of the agreement is extremely grave, particularly at this time of instability in Syria. Following the incident, Israel filed a formal complaint with UN Secretary General Ban Ki-moon and with the Columbian Ambassador to the UN and current Security Council President Nestor Osorio.

"Excellency, I write to draw your attention to an alarming development in our region," Israel's Deputy Ambassador to the UN Haim Waxman wrote. "On 19 July 2012, in the midst of fighting between Syrian security forces and other armed elements near the Syrian village of Jubata Al Khashab, Syrian soldiers crossed into the area of separation under the 1974 Separation of Forces between Israel and Syria."

The deputy ambassador noted that this was a blunt violation "of this agreement, with potentially far-reaching implications for the security and stability of the region. Waxman added that Israel is very concerned by the actions of the Syrian army in the separating area.

"The security council should address this alarming development with great seriousness," he concluded.

According to a source at the Foreign Ministry, Israel's UN delegation held meetings throughout Thursday with the division of the UN peacekeeping forces, during which it emphasized the urgency of the matter. Following the talks, the UN Observer Force distributed a letter, of its own, confirming Syrian troops had entered the demilitarized zone.

The UNDOF commander said he had approached the Syrian army and given them the Israeli message, along with the UN protest over the Syrian violation.

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