Twelve Syrian security forces were killed in an ambush by a group of defecting soldiers in the town of Dael in Daraa province, the opposition Syrian Observatory for Human Rights said.

The security forces were entering the town from the south to start a campaign of arrests when they were ambushed, the observatory said. Five of the defectors were wounded in clashes with other Syrian security forces who had arrived to evacuate the dead, the group said.

Syria, on the state-run Syrian Arab News Agency, said 17 army and law enforcement "martyrs" were buried Tuesday.

The regime got fresh backing from Russia for its assertion that terrorist groups are behind the widespread violence.

Russian Foreign Minister Sergey Lavrov, at a news conference, said that if reports of an al Qaeda presence in Syria prove true, "and I assume it is the case, then the weapons coming to Syria could fall into the hands of this terrorist organization." And he noted that, according to a U.N. Security Council resolution, all U.N. members "should not only prevent weapons from getting to al Qaeda, but must avoid all links."

Al-Assad, who has insisted he is helping lead democratic reforms, has set May 7 for parliamentary elections, the Syrian parliament website said Tuesday.

But many world leaders and opposition activists have said al-Assad is leading a violent crackdown aimed at keeping his lock on power.

The opposition Syrian National Council called Monday for urgent international military intervention to help stop the violence and to protect civilians.

The council, an umbrella group that includes opposition members abroad as well as dissidents inside Syria, also demanded a no-fly zone across the country and a "speedy operation" to arm the Free Syrian Army, rebel fighters composed primarily of defectors from al-Assad's forces.

"Sympathy messages are no longer enough. ... What is needed is actions on (the) ground and decisions and measures against (al-Assad's) gangs," the group said after a meeting in Turkey.

Yousuf, a resident and opposition activist in Homs, described incessant bombings across the city Tuesday.

"There have been over 100 explosions heard in Homs this morning caused by the continuous tank shelling and rockets" in several neighborhoods, said Yousuf, who is not being fully identified for safety reasons.

About 30,000 Syrians have fled to neighboring countries in the past year, according to Panos Moumtzis, the U.N. High Commissioner for Refugees' coordinator for Syrian refugees.

Even the flight abroad is fraught with danger, according to Human Rights Watch.

Syrian forces have placed landmines near the borders with Turkey and Lebanon, the group said Tuesday, citing witnesses and Syrians who have helped remove them.

"The Syrian army should cease its use of antipersonnel landmines and recognize that planting this internationally banned weapon will hurt Syrians for years to come," Human Rights Watch said. "Both antipersonnel and antivehicle mines of Soviet/Russian origin have been cleared by deminers associated with the opposition."

CNN cannot independently confirm reports of casualties or attacks in Syria because the government has severely restricted the access of international journalists.

But most reports from inside Syria indicate the regime is slaughtering civilians to wipe out dissidents seeking al-Assad's ouster. The al-Assad family has ruled Syria for more than four decades.