The Syrian military launched a two-pronged attack on the northern city of Aleppo Wednesday, with jets and helicopters bombing from overhead while ground forces targeted rebel positions.

Syrian state television said government forces were overrunning the rebels, but the leaders of the opposition's Free Syrian Army denied they were retreating. Reports from foreign journalists in the city said that some rebels had indeed pulled back.

The Syrian Observatory for Human Rights described the latest fighting as the most violent since rebels claimed control of part of the city. The group said more than 300 people have died across Syria in the last two days.

Rights group Amnesty International has released satellite images of Aleppo and the surrounding areas, showing what it says are signs of increased heavy weapons usage.

The group says the images raise “urgent concerns” about the assault on the area. It also warns both rebels and government forces that attacks against civilians will be “clearly documented.”

Syrian President Bashar al-Assad has vowed to purge his country of what he calls “terrorists.”

Iran's foreign minister says some of the 48 Iranians held by Syrian rebels are retired members of the Revolutionary Guards and the army, and were in Damascus on a religious pilgrimage.

Iran's ISNA news agency quoted Foreign Minister Ali Akbar Salehi as denying that the Iranians have any current military connection.

The rebel Free Syrian Army describes those kidnapped last Saturday as Revolutionary Guards on a “reconnaissance mission.”