A massive explosion Wednesday targeted a Syrian government intelligence building in central Syria, leaving at least five soldiers dead, reported Syrian opposition activists, dpa reported.
"The blast was the result of a suicide attack at the intelligence headquarters in Palmyra," said Rami Abdul-Rahman, the head of the Syrian Observatory for Human Rights.
"It was followed by a clash between the troops manning the headquarters and the attackers," he added.
Palmyra, a World Heritage site famous for Roman ruins, is in the restive province of Homs.
The ancient city, once a major tourist attraction, has been affected by a 22-month conflict between President Bashar al-Assad's troops and opposition rebels fighting to oust him.
Elsewhere, the army was stepping up a campaign on areas held by radical rebel groups, mainly the Jihadist al-Nusra Front, on the outskirts of the capital Damascus and the northern province of Aleppo, a military source and activists told dpa.
Abdel Rahman said the Syrian army had sent heavy reinforcements to the areas where al-Nusra is believed to have strongholds.
Al-Nusra is described by military observers as "the most aggressive arm" of rebel forces in Syria.
The United States has labeled the group as a terrorist organization.