UNITED NATIONS, Sept 17 (Reuters) - August was the worst month for casualties so far in Syria's 18-month conflict, the United Nations said on Monday, warning that the worsening "grim spiral of violence" could threaten the country's neighbors.
U.N. Special Coordinator for the Middle East Peace Process Robert Serry did not give specific figures, but the world body says about 20,000 people have died during the conflict, including a record toll of 1,600 for the final week of August.
"The month of August registered the highest number of casualties thus far, and this toll is growing," Serry said.
More than 250,000 Syrians have fled to neighboring Turkey, Jordan, Lebanon and Iraq to escape the violence - with more than 100,000 of those leaving in August alone.
"Tragically for millions of Syrian civilians the violence and killing continue to mount as a result of a dangerous militarization of the conflict," Serry told the U.N. Security Council as he briefed them on the situation in the Middle East.
"Military operations have broadened, encompassing all major cities. Indiscriminate shelling of civilian areas by government forces with heavy weapons, tanks and air assets has increased. Operations from the armed opposition have intensified," he said.
International mediator Lakhdar Brahimi met with Syrian President Bashar al-Assad on Saturday for the first time since he replaced Kofi Annan as the U.N.-Arab League representative. Brahimi said the escalating conflict posed a global threat.
Serry also said that "as conditions deteriorate, we see dangerous implications for Syria's neighbors," referring to the growing number of refugees and the violence that has sporadically spilled over the borders.
The revolt in Syria started as a mainly peaceful street campaign for reform but has become a bloody insurgency that is deepening sectarian rifts in the Middle East.
World powers are deadlocked in the U.N. Security Council along Cold War lines, with the United States and its NATO allies supporting the call for Assad to quit and Russia and China defending him against what they see as outside meddling.
Moscow and Beijing have three times blocked Western-backed attempts in the Security Council to criticize Damascus and threaten sanctions against it.
Annan blamed the Security Council impasse for hampering his six-month bid for peace and leading to his decision to step down at the end of last month. Brahimi has described his mission of trying to broker a peace deal as "nearly impossible."