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A group of 20 internally displaced people were killed on Wednesday when a barrel bomb was dropped by the Syrian airforce on a refugee camp in the northwest of the country.

They had been seeking shelter in a refugee camp near the village of Abdin in Idlib province when troops dropped the bomb, a relatively inexpensive weapon whose lack of precision often results in civilian casualties.

The camp has around 200 tents, and is set in the olive trees of the surrounding area.

The al-Nusra Front, the Syrian wing of al-Qaeda, are battling for control of Idlib province against the Syrian Revolutionaries' Front (SRF), an affiliate of the rebel Free Syrian Army.

On the offensive

Asad Kanjo, an activist from Idlib, said that the al-Nusra Front, aided by another armed group named Jund al-Aqsa, seixed seven villages in the province on Tuesday. The fighting reached the major rebel-held town of Maaret al-Numan, he added.

Kanjo said that the battles began on Sunday after a small group defected from SRF and joined al-Nusra with their weapons. A wide-ranging offensive was subsequently launched, leading to the capture of the seven villages.

Idlib is split between Syrian government and rebel controlled areas, with the provincial capital, also named Idlib, under the control of the regime of President Bashar al-Assad.

Divided opposition

Although anti-Assad groups including both al-Nusra and the SRF come from different ideological standpoints, they have largely avoiding fighting each other, concentrating on taking on Assad forces or the Islamic State group (IS, formerly known as ISIS).

However, US-led coalition airstrikes against IS have also targeted the al-Nusra Front, something that appears to have brought the two groups closer in recent weeks.

On Monday, al-Nusra and its affiliated rebel groups attacked Idlib city, leaving at least 35 government troops and rebels dead. The attacks were the most dangerous since rebel factions took control of most of the rest of the province more than two years ago. Government forces have held out in the city of Idlib, resupplied by airdrops from Damascus.

Rami Abdel Rahman, the director of the London-based opposition group, the Syrian Observatory for Human Rights, said that sleeper cells inside the city had been activated as al-Nusra attacked Idlib from the suburbs.

"Police officers, backed by sleeper cell members of al-Nusra - already inside the city - attacked the governorate building but they were quickly pushed back by regime forces," said Abdel Rahman.