Egypt on Monday began to release detainees held by the military following a decree last week by President Mohammed Morsi, security officials told Agence France Presse.

"Prison authorities have begun releasing the detainees," an official told AFP.

At least 23 people were "summarily executed" by regime forces in two Damascus neighborhoods on Sunday, the head of the Syrian Observatory for Human Rights watchdog told Agence France Presse on Monday.

"Sixteen people, most of them younger than 30, were summarily executed by shooting on Sunday in Mazzeh," Observatory chief Rami Abdel Rahman said, referring to an upscale district in western Damascus.

Syria will not use chemical or other unconventional weapons except in the case of a foreign attack, foreign ministry spokesman Jihad Makdissi said on Monday.

"Syria will not use any chemical or other unconventional weapons against its civilians, and will only use them in case of external aggression," Makdissi told a media conference in Damascus.

The European Union on Monday tightened sanctions on Syria and required member nations to board ships and airplanes carrying suspicious cargo to the country.

The 27 EU ministers added 29 names to an existing list of over 170 Syrian individuals and companies believed to be associated with the repression, or benefiting from President Bashar Assad's regime.

As tens of thousands of Syrians flee escalating war and chaos, the EU looked at ways of boosting humanitarian relief and beefed up sanctions and an arms embargo against the regime Monday.

Joining talks with their European Union counterparts, the foreign ministers of Britain, France and Sweden called for a hike in aid to Syrians who have fled to safety in neighboring Jordan, Lebanon and Turkey.

Arab foreign ministers have backed Palestinian plans to seek an upgrade to their status at the United Nations to that of a non-member state, Palestinian officials said.

But no decision was taken on when the application would be made, with the Arab League postponing such a decision until its next meeting in Cairo on September 5, Palestinian negotiator Saeb Erakat told Agence France Presse late on Sunday.

A plume of black smoke rose over the Mazzeh neighborhood of Damascus on Monday as activists reported clashes during the night across the capital as well as in Syria's second city of Aleppo.

Residents of Damascus reported hearing gunfire and explosions into the early hours of the morning in the upscale Mazzeh neighborhood of west Damascus, while activists reported overnight shelling in several other districts of the city.

The Syrian National Council sounded a defiant note in a an overnight statement, saying fierce clashes in cities across the country was a sign the opposition was "at the gates of victory."

SNC spokesman George Sabra said in the statement the heavy fighting that has broken out in Damascus and the country's second city Aleppo in recent days was an important sign of rebel progress.

The U.S. government has been quietly trying to block arms and oil shipments from Iran to Syria in a bid to accelerate the fall of Syrian President Bashar Assad, The Wall Street Journal reported late Sunday.

Citing unnamed U.S. officials, the newspaper said the efforts are aimed at getting Iraq to close its airspace to flights between Iran and Syria that U.S. intelligence believes are carrying arms for Syrian pro-government forces.

The situation in Syria is "calm," requiring no repatriation of Iranian citizens there, Iranian Foreign Minister Ali Akbar Salehi said on Sunday, according to the official news agency IRNA.

"Syria is calm and Iranian nationals who are there have no problem and there is no need to conduct any special action" for them, Salehi was quoted as saying.