UN Secretary-General Ban Ki-moon on Thursday voiced his deep concern over the continued armed escalation in Syria, condemning the indiscriminate use of any weapon against civilians.

The UN chief is "following with deep concern the continued armed escalation in Syria, most deplorably the ongoing aerial attacks and the use of 'barrel bombs' to brutal, devastating effect in populated areas," said a statement issued by Ban's spokesperson.

Ban has spoken out against the use of so-called "barrel bombs" -- oil drums filled with explosives and shrapnel and dropped from aircrafts -- and reiterated his condemnation of indiscriminate use of any weapon against civilians, in contravention of obligations under international law.

"All civilians must be protected in any situation," the statement said, underscoring that the Secretary-General also reiterates further violence serves the agendas of those who see military means as the only way forward, at the expense of the Syrian people.

"He appeals to all Syrian sides to work immediately on reducing the levels of violence and focusing on a peaceful solution to the conflict," it said.

According to reports, the Syrian army dropped barrel bombs Tuesday on a mosque in Aleppo, killing at least 11 people. Dozens of people were killed by barrel bombs in the northwestern Syrian city last week.

The first round of peace conference known as Geneva II ended in late January in Switzerland without any fruitful solution to the on-going conflict in Syria, which has killed more than 130,000 people in the past three years.

About 8 million have been driven from their homes in the war-torn country, with 2 million of them seeking refuge in neighboring countries, since the conflict erupted in March 2011 when originally peaceful protestors sought the ouster of President Bashar al-Assad.