Sana’a: Yemeni police fired tear gas on Tuesday to quell a prison riot by inmates held on terrorism charges in the capital, leaving at least three in critical condition, a security official said.

The officials said dozens of inmates linked to Al Qaida refused to return to their cells, chanting and scuffling with the prison guards. Police fired their weapons into the air and lobbed tear gas in response. The officials said at least nine inmates were wounded, including three critically.

A security official said troops deployed outside the prison in Sana’a, fearing militants could take advantage of the commotion to storm it. The officials spoke on condition of anonymity because they were not authorised to talk to the media.

However, a government statement said that prisoners stabbed a chief investigator and a number of guards before rioting and breaking the prison gates. It denied there were casualties among the prisoners.

It was impossible to reconcile the two accounts.

Yemen is fighting a war against Al Qaida’s local branch, considered by Washington to be one of the world’s most dangerous offshoots of the terror network.

The branch, also known as Al Qaida in the Arabian Peninsula, regularly strikes security and military targets with drive-by shootings, suicide bombings and other attacks.

In August, the group’s leader Nasser Al Wahishi, a one-time aide to Osama Bin Laden, posted a message vowing to free fellow militants from prisons and urged jailed fighters to remain faithful to the terror group’s ideology.

He addressed his message to “prisoners who are in the jails of the oppressors because of their religion” and told them to “rejoice ... as your brothers are pounding the walls of injustice and demolishing the thrones of oppression... We have not forgotten you and will never forget you”.

Al Wahishi, himself a former prisoner, fled from a detention facility in Sana’a with more than 20 Al Qaida militants in February 2006, in a major prison break.