The blasts were apparently sparked by rebel rocket fire, which struck the ammunitions depot, according to the Britain-based Syrian Observatory for Human Rights. It said 40 people were killed and 120 wounded, some critically.

The weapons explosions occurred in the pro-regime district of Wadi al-Zahab, operated by militias loyal to the regime of Syrian president Bashar al-Assad. An activist video posted online shows a huge fire ball over Homs neighborhoods.

An official at the Homs governor's office, speaking on condition of anonymity to news agency AP, said 10 rockets slammed into a nearby neighborhood and sports stadium, sparking a large fire. A Homs resident said blasts could be heard from the pro-regime districts of Wadi Dahab and al-Walid, where the regime is known to keep arms depots.

The resident said the explosions were so strong that "they shook parts of the city."

Other areas, including Akruma and Al-Nozha, are believed to have also been hit. These districts are mainly inhabited by members of al-Assad's Alawite community.

Homs, which is located 140 kilometers (85 miles) north of Damascus, is seen as a key city in the battle for the control of Syria, as it is situated at a strategic crossing point that links the capital with army bases near the Mediterranean coast.

According to UN estimates, more than 100,000 people have been killed in Syria since early 2011, when the uprising began with peaceful protests to demand political reforms.

Thursday's blasts and rocket fire in Homs follow the Syrian regime's capture of the Khalidyeh district on Monday, that had been in the hands of mainly Sunni rebels for the past two years.

jr/hc (Reuters, AFP, AP)