The youths stormed La Terrasse restaurant near the capital, Manama, on Wednesday night because it was serving alcohol, the owner said.

Customers said one diner managed to grab hold of a knife and he stabbed one of the youths with it.

Bahrain allows bars and restaurants to sell alcohol, but this has recently prompted protests by Islamic activists.

The owner of La Terrasse, Jahanshah Bakhtiar, told the Reuters news agency that there were about 40 customers in the restaurant at the time of the attack, including seven Westerners.

He said: "About 100 young men, shouting 'God is great', came to the restaurant carrying knives and shouted at the customers, 'Why do you drink?'"

The stabbed youth was taken to hospital and was reported to be in a critical condition.

The attackers also threw petrol bombs at cars parked outside the restaurant, damaging seven of them.

A Bahraini interior ministry official told local media that police had arrested a number of youths following the incident.