Air strike kills at least 39 in al-Qaeda affiliate run prison in northwestern Syria

Human rights groups said the missiles also hit an Islamic Court attached to the prison and nearby road

An injured woman is carried away from the wreckage of the prison in Maaret al-Numan (Reuters)

A Russian air strike has killed at least 39 people at a prison run by an al-Qaeda affiliate group in Syria, activists have said.

The London-based Syrian Observatory for Human Rights has said at least 39 people have been killed but another group - the Local Coordination Committees - has said the death toll is at 51.

Agence France Presse has reported that five civilians were among the dead - including a child.

The Observatory said four missiles hit an Islamic Court attached the jail as well as a nearby road that connected the court with a nearby market.

Others killed included many fighters from the al-Nusra Front as well as detainees of the prison in the northwestern town of Maarat al-Numan.

The al-Nusra Front is one of the many non-Isis jihadist groups operating in Syria which are being targeted by Russian air strikes.

Several opposition groups control territory in the north west corner of Syria - including Idlib and parts of Aleppo - but Syrian government forces are advancing in part due to the intervention of Russia.

Around 70 per cent of the 5,000 air strikes reportedly carried out by Russia since they launched their offensive in September last year have hit Isis controlled targets, an US official told reporters.

Human rights groups and aid agencies have also accused Russia of killing civilians in markets and residential areas during its "imprecised" campaigns - this is a charge Russia has denied.

UK forces began air strikes against the country at the end of last year but have so far focused on targeting Isis controlled areas.

Isis and al Nusra are bitter rivals despite both being hardline Islamist rebels fighting against the Assad government.

Additional reporting by agencies