Saudi Arabia is proposing a U.N. General Assembly resolution which will highlight a Syrian government threat to use chemical weapons, its U.N .envoy said Wednesday.

The new Arab initiative follows the failure of a western-attempt to get the U.N. Security Council to threaten sanctions against Syria's President Bashar Assad over the 16-month-old conflict, diplomats said. Russia and China vetoed the council resolution last week.

Saudi authorities on Wednesday temporarily freed a protester on trial after having been detained last year when he arrived at the site of a planned anti-government demonstration, activists told Agence France Presse.

"Khaled al-Johani was released for 48 hours during which he will remain under surveillance," an activist said, adding that his trial would continue.

The United States on Wednesday condemned Syria's use of attack helicopters in its civil conflict as "another indication of the depth of depravity" of the regime of President Bashar Assad.

White House spokesman Jay Carney issued the reaction aboard Air Force One following reports that helicopter gunships strafed several neighborhoods in Aleppo, Syria's commercial capital.

Russia is ready to host talks between the Syrian opposition and President Bashar Assad in a bid to end the country's conflict, its U.N. envoy said Wednesday.

Ambassador Vitaly Churkin made the offer as he stepped up Russian attacks on the United States and European countries for saying they will seek to increase pressure on Assad outside of the U.N. Security Council.

Having fled a city where shells fell "like rain" and children died in front of them, Syrian refugees spoke of the hell that would erupt every night as troops sought to retake their border town.

Wearing a dirt-covered dishdasha, or traditional Arab robe, his face pale from exhaustion, Ahmed Saleh Hanoush sat on the floor of a school-turned-dormitory for refugees, fighting back tears.

"You've got to be prepared for anything with what's going on in Syria," said Benny Rahamim, one of a growing number of Israelis picking up gas masks as fears grow over Syria's chemical weapons.

Rahamim, 36, was visiting a mall in the dormitory town of Mevasseret Tzion, just outside Jerusalem, one of many locations nationwide where the postal service runs distribution centers for gas masks.

A high-level Syrian economic delegation led by Deputy Prime Minister Omar Ghalawanji arrived in Tehran on Wednesday to boost cooperation between the two allies faced with Western economic sanctions.

Iran's official news agency IRNA said the visiting team included the ministers of oil, electricity, health, water and housing.

Up to 50 members of the Syrian opposition are working in Berlin on plans for a political transition after a possible ouster of President Bashar Assad, a German think tank backing them said Wednesday.

The respected German Institute for International and Security Affairs (SWP) confirmed a media report that it was working with the group of former generals, economists and legal experts on what could become a new constitution.

U.N. chief Ban Ki-moon on Wednesday urged the world "to stop the slaughter in Syria" as dozens of international observers pulled out from the country.

"I make a plea to the world: 'Do not delay... Act now to stop the slaughter in Syria'," the U.N. secretary-general told parliament in Bosnia, the Balkans country that suffered a genocide in Srebrenica in 1995.

Amnesty International warned on Wednesday about disturbing reports of "summary executions" by Syrian troops and rebels, calling them "serious violations of international law."

In a statement, the rights watchdog cited reports from media and local activists on instances in which both Syrian government troops and rebel forces have carried out summary killings.