Montevideo, Feb 7 (IANS/EFE) Close to 400 inmates tried to escape from a prison outside Montevideo during a massive brawl between two groups of inmates, the daily Ultimas Noticias said Saturday.

The incident required the intervention of an elite National Police unit known as the GEO, which rushed to help the 15 prison guards on duty when the fight broke out, and which ended with one seriously injured convict being taken to hospital.

Why the brawl started is still unknown, according to the daily, though penitentiary officials quoted in the newspaper believe it was due to the overcrowded living conditions inside the jail.

Apparently it all began when some 60 inmates belonging to two different gangs started a fight in the prison courtyard, several of them armed with knives they had made themselves in jail.

As the battle unfolded, another 400 inmates who were in the courtyard at the time tried to get away by opening one of the prison gates amid the confusion.

The intervention of prison guards and their reinforcements from police and the GEO, who cordoned off the outside of the prison, kept the jailbreak from succeeding.

Friday afternoon a search of the Comcar prison on the outskirts of Montevideo led to the seizure of a grenade, almost 500 gram of marijuana, 35 knives and 30 liters of homemade alcohol.

In the same prison less than 10 days ago the authorities found a grenade, a handgun and more than 200 knives.

Human rights are 'systematically violated' in Uruguayan prisons due to the degrading conditions and overcrowding in which the inmates live, according to a recent report published by the United Nations.

The miserable conditions make inmate riots and protests a common occurrence.

The government announced in April of last year a plan to immediately combat overcrowding in jails, which included the transfer of 1,250 prisoners to new detention centres set up in government buildings, including barracks and hospitals.

According to 2007 figures - the latest available - Uruguay's prison population totals about 8,000 inmates.