Civil strife in Syria is peaking, and the fighting has moved from the countryside and smaller cities to the nation's two most urban centers, Damascus and Aleppo. Aleppo is a commercial hub and has traditionally been a bedrock of support for President Bashar Assad.

Colonel Abdul-Jabbar Mohammed Aqidi, the commander of rebel forces in Aleppo province, said in a video shown on YouTube: "We gave the orders for the march into Aleppo with the aim of liberating it."

The Britain-based Syrian Observatory for Human Rights and Aleppo-based activitist Mohammed Saeed said rebels are concentrating on several neighborhoods in Aleppo and that they control the central Salaheddine district and nearby Sakhour area.

In an effort to gain some momentum, the rebels have also sought to take control of several border crossings with Iraq and Turkey. In recent days, this has led to them taking control, then losing it to Assad's forces, and retaking it. In the latest development, for example, rebels were shown in a video in front of the Bab al-Salamah crossing on the Turkish border raising a Syrian opposition flag.

Brigadier General Manaa Rahal of the Free Syrian Army said three border crossing were in rebel hands, including two along the Turkish border and the Bab al-Yarubiyeh crossing near Iraq.

The current fighting in Aleppo comes days after violence erupted in several districts of Damascus, which included a bombing that struck directly into the core of Assad's inner circle, killing four senior officials.

Aleppo's Old City is listed among UNESCO's world heritage sites and is one of the world's oldest and continually inhabited cities.

In Damascus, meanwhile, Syrian troops led by Assad's brother bombarded rebel areas with helicopter gun ships in an attempt to drive the rebels out of a northern district.

Syrian state TV played down the levels of violence, saying that Assad's troops were hunting and killing "terrorists".

July is shaping up to be the deadliest in the 16-month-old uprising. The Syrian Observatory for Human Rights said 1,261 people had been killed across Syria since last Sunday. Overall, the conflict has claimed the lives of 19,000 people.

tm/ng (AP, AFP, Reuters)