Anti-regime groups have entered the city center of Syria's regime-held Aleppo, the head of a war monitor said Friday.

Hayat Tahrir al-Sham (HTS) and allied factions "are now in the southwestern and western neighborhoods of Aleppo city," said Rami Abdel Rahman, who heads the Syrian Observatory for Human Rights. Two Aleppo residents told AFP they saw gunmen in their neighborhoods, as panic gripped Syria's second-largest city.

The anti-regime armed groups, which had been advancing toward Aleppo from the west after clashing with regime forces for three days, broke through the defense lines in the Hamdaniyya, New Aleppo, and Zahra axes in Aleppo's western countryside and entered the city center.

After three days of fighting in Aleppo and Idlib provinces, opposition groups are said to have taken control of 400 square kilometers (154 square miles) of territory.

Following fighting carried on through the night, opposition forces advanced on the outskirts of the city, seizing control of 70 settlements and strategic locations.

Approximately 10,000 civilians fleeing the fighting have sought refuge in rural Idlib.

Control of Saraqib secured

Armed opposition and anti-regime groups in Syria have entered the strategically important town of Saraqib in Idlib, local sources reported.

During two days of clashes in Idlib, regime forces suffered heavy losses and withdrew from Saraqib. The town is now under the control of anti-regime armed groups.

Saraqib is located strategically at the intersection of the M4 highway, which connects the capital Damascus to Aleppo, and the M5 highway, which links Latakia to Aleppo.

Fighting spreads to Aleppo's suburbs

Clashes are intensifying in the outer suburbs of Aleppo, prompting numerous regime loyalists to flee from Aleppo to Damascus.

The armed groups captured the Scientific Research Center located in one of Aleppo's outer neighborhoods.

This facility had been used for military purposes by the regime and reportedly produced barrel bombs and artillery batteries.

The groups also seized Anadan, one of the largest settlements on the outskirts of Aleppo.

As of Friday morning, anti-regime forces have gained control of nearly 550 square kilometers (342 square miles) of territory along the Idlib and Aleppo front lines.

The forces have also captured numerous villages and positions in Aleppo's western countryside.

Russian warplanes carried out an airstrike early Friday on an opposition headquarters in the northern Syrian town of Mare. The attack reportedly caused material damage but no casualties.

The Assad regime targeted civilian areas with ground-to-ground weapons during the ongoing clashes.

Dozens of regime soldiers captured

Anti-regime armed groups have seized heavy weapons, military depots, and vehicles from regime forces in the areas they captured.

Many regime soldiers were killed in the fighting, and dozens were taken prisoner.

4 students killed in Syrian regime attack on university dormitory in Aleppo

Four students were reportedly killed and two others injured on Friday in a missile attack by Syrian regime forces on a student dormitory affiliated with the University of Aleppo.

Local sources reported that the attack targeted the dormitory amid ongoing clashes between regime forces and opposition groups on the outskirts of Aleppo.

The regime has not yet issued a statement on the attack.

Syria has been embroiled in a vicious civil war since early 2011, when the Assad Syrian regime cracked down on pro-democracy protests with unexpected ferocity.

The attacks of recent days are some of the fiercest fighting the conflict has seen in years.