The Arabic daily said road patrols in Madinah arrested a Yemeni who tried to smuggle the explosives, which were concealed in detergent cartons into the city.

The man justified his possession of the explosives by saying he used them for legitimate excavation work, the paper said.

In another development, police in Tathleeth in the southern Asir region foiled another attempt to smuggle 50,000 pieces of ammunition in a car.

Security officers are investigating the driver of the car for allegedly trying to smuggle the ammunition into the Kingdom, Al-Watan said.

Saudi Arabia is on high alert following the May 12 terrorist attacks against three residential compounds in Riyadh in which 34 people were killed and almost 200 injured.

According to Al-Watan, more than 80 checkpoints have been established in Jeddah alone following reports that the Al-Qaeda network was planning attacks in the Red Sea port city.

The measure was taken to prevent terrorists from bringing explosives and weapons into the city. Security has been beefed up at major hotels and residential compounds.

The Civil Defense Department said it had heightened security alert to the maximum and increased safety patrols.

The department has also assigned extra officers and equipment to meet any emergency situation, the paper said.

The department developed an emergency plan in coordination with Jeddah Municipality, the Health Ministry and the Saudi Red Crescent Society.

The Riyadh bombings came a week after police seized a huge stash of explosives, weapons and cash following a shootout with suspected terrorists in a residential district in the capital.

The Interior Ministry at the time said police were hunting 19 terrorists including 17 Saudis who intended to carry out major attacks in the Kingdom.

The May 12 bombings constituted one of the largest attacks by militants in the Kingdom since the 1991 Gulf War.

In November 1995, five Americans and two Indians were killed and 60 people were injured in an explosion in a car park near a US-run military training center in Riyadh.