At least 20 Syrian soldiers have died in twin suicide bombings in the nation's south.
Saturday's early morning blasts in Deraa targeted an encampment for forces loyal to Bashar al-Assad, the Syrian president, in the city, according to the Syrian Observatory for Human Rights.
"I heard two very loud explosions and a third smaller one followed by bursts of gunfire," said Mohammad Abu Houran, an activist in Deraa.
He said the first two were likely car bombs and the third a mortar shell or rocket propelled grenade.
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The Britain-based observatory said the explosions were followed by clashes between forces loyal to Damascus and opposition fighters wanting to topple al-Assad.
Rami Abdul-Rahman, chief of the monitor group, said the 20 deaths had yet to be independently verified.
State-run news agency SANA said the explosions caused multiple casualties and heavy material damage, but did not provide further details.
Abu Houran said black smoke could be seen over the high-security area, which was sealed off. Heavy shooting could be heard from the area for about 10 minutes after the explosions, he added.
The targeted area is considered a security zone that houses a branch of the country's Military Intelligence as well as an officer's club where dozens of al-Assad forces are based.
Around 30 tanks that government forces use to shell Deraa and surrounding areas are also stationed in a nearby stadium, activists said.
Deraa was the birthplace of the uprising against Assad, which erupted in March 2011.
The Deraa bombings come a day after as many as 11,000 people were said to have fled Syria over just 24 hours, to escape fierce fighting between opposition fighters and government forces - the latest surge of refugees fleeing the civil war.
The flood of Syrians into neighbouring Turkey, Jordan and Lebanon was "the highest that we have had in quite some time," said Panos Moumtzis, regional co-ordinator for the United Nations High Commissioner for Refugees.
About 2,000 to 3,000 people are fleeing Syria daily, and the recent surge brings the number registered with the UNHCR to more than 408,000, Moumtzis said.
The largest flow into Turkey came from the fighting at Ras al-Ayn in the predominantly Kurdish oil-producing northeastern province of al-Hasaka, where the opposition was fighting government forces.