A bomb explosion rocked the heart of the Syrian capital on Wednesday, killing at least eight people and wounding 50 others, state media reported.
The blast came as rebels seized parts of a key arms depot in the central province of Homs and regime forces recaptured most of the Kurdish town of Tal-Aran in the northern province of Aleppo, a monitor said.
Also in Aleppo, fighters from the Al-Qaeda-affiliated Islamic State of Iraq and the Levant (ISIL) seized a major power plant, said the Syrian Observatory for Human Rights.
The blast in central Damascus hit Al-Hijaz Square, killing eight people including two women.
State news agency SANA said it was caused by a bomb placed at the entrance to the Hijaz railroad company and that more than 50 people had been wounded, among them women and children.
In Homs province, the Observatory said rebel forces had taken over parts of an arms depot, though a security official in Damascus denied the insurgents had advanced or seized weapons, saying the fighting was ongoing.
The conflicting reports come just over two weeks after jihadists and other rebels launched a major offensive aimed at capturing one of Syria's largest weapons depots, near Mahin in the Homs countryside.
The fight for the depot left more than 50 rebel fighters and 20 loyalists dead on Tuesday alone, the Observatory said.
Fighters from Al-Nusra Front and ISIL -- both linked to Al-Qaeda -- and the Al-Khadraa and Baba Amr Commandos battalions "took over buildings of an army weapons depot near Mahin," the group said.
The rebels "seized a large amount of weapons" in the complex, which comprises some 30 buildings, it added.
The regime security official denied the report, saying: "The battle is continuing. The terrorists did not take any weapons, and there are many losses in their ranks."
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The Syrian government refers to all the rebels battling to overthrow President Bashar al-Assad as "terrorists".
Elsewhere, the Observatory said regime forces had taken control of most of the town of Tal-Aran, which is strategically located on the main road between Aleppo city and the town of Sfeirah.
Sfeirah is near a military site believed to hold some of the regime's chemical weapons, and was recaptured by the army last week.
On Wednesday ISIL fighters took control of the nearby Aleppo power plant.
The capture raised fears the group could cut electricity supplies to other parts of the city. Only regime-held parts of Aleppo still receive power from the plant.
Much of Aleppo has been destroyed by army bombardment and fighting since a massive rebel advance on the city in July 2012.
The Observatory also reported a large car bomb blast near an air force intelligence facility in the southern province of Sweida, but there was no initial information on casualties.
Elsewhere, ISIL fighters vandalised a statue in the northern city of Raqa, the only provincial capital under opposition control.
Fighters decapitated the male and female peasants depicted in the statue, known locally as the Statue of Liberty, the Observatory said.
More than 120,000 people have been killed in Syria's 31-month conflict, and millions more forced to flee their homes.
The armed uprising flared after President Bashar al-Assad's forces launched a brutal crackdown on peaceful protests inspired by the 2011 Arab Spring.