**Thirteen inmates escaped when armed men arrived in 10 vehicles and stormed a prison in the border city of Reynosa, Mexican officials have said.**Three prisoners died during the raid but it was unclear who shot them.
Authorities have put 31 prison staff under investigation in connection with the escape.
It was the second big jailbreak in a week in Tamaulipas state, which has seen an increase in violence blamed on a split between rival drug gangs.
The jailbreak in Reynosa, which lies just across the US-Mexico border from McAllen in Texas, happened on Friday night. The authorities reported the raid and the deaths of the three prisoners but did not give details of the escape until Sunday.
On 26 March, 40 prisoners escaped from a jail in Matamoros, also in Tamaulipas.
Escapes are common from Mexican state prisons, with guards either being paid to assist or intimidated into not resisting.
Violence has been on the increase in Tamaulipas and in the neighbouring state of Nuevo Leon.
Officials say the powerful drug-trafficking gang known as the Gulf Cartel has split with its former allies, Los Zetas, and the two are now battling for control of drug routes into the US. This article is from the BBC News website. © British Broadcasting Corporation, The BBC is not responsible for the content of external internet sites.