Story highlights

Clashes have been constant in the Damascus suburb

Every time rebels advance, the regime steps up offensive, groups say

U.N. warns that all sides will be held accountable for the killing of civilians

CNN  — 

A car bomb exploded near a police station in northeastern Damascus on Sunday, killing at least eight members of the security forces, the Syrian Observatory for Human Rights said.

The blast also wounded an specified number of civilians, the group said.

The explosion took place during heavy clashes between rebel forces and regime troops in Jobar, a suburb of Damascus, where clashes between the two sides are constant.

MORE: ‘Eyes of world’ on Qusayr battle, says U.N.

“If we capture the area it means we have reached the heart of the capital. It means we can cross into Damascus,” a spokesman for the local Revolutionary Military Council said in March.

But every time rebels appear to be inching closer to a decisive battle for the capital, President Bashar al-Assad’s stronghold, the regime steps up its offensive using fighter jets and missiles to shell the suburb, opposition groups say.

The United Nations has warned that all sides will be held accountable for the killing of civilians during the civil war.

‘Open-ended’ Syrian conflict draws in region

Battles between the two sides have raged, including in the besieged Syrian border city of Qusayr, where government forces and Hezbollah fighters have been battling rebels for control.

U.N. chief Ban Ki-moon warned forces loyal to al-Assad and rebels to allow civilians to leave the town, the latest flashpoint in the more than two-year-old conflict that has left about 80,000 people dead.

“The eyes of the world are upon them, and they will be held accountable for any acts of atrocity carried out against the civilian population,” Ban said.

As many as 1,500 people are believed to be wounded and in need of medical care in the border town.

Reports: Russian fighter jets headed to Syria, which asks for more