Bahrain police found a bomb planted on a causeway linking the island to Saudi Arabia, and four officers were shot and wounded late on Friday, officials said.

The 2 kg bomb, discovered near a mosque on the Bahraini side of the route used by thousands of people every day, was safely defused after a cleaner alerted the police, said the kingdom's Information Authority.

"The operations room was alerted at 4pm on Thursday after a cleaner got suspicious of the strange object," Public Security chief Major-General Tariq Al Hassan said.

Explosive experts rushed to the scene and defused the bomb which contained a highly explosive substance and other solid materials.

The Public Prosecution has launched an inquiry to track down the perpetrators and bring them to justice, he said.

Maj-Gen Al Hassan called upon citizens and residents not to tamper with strange objects and report any suspicious case on hotline 999.

Also four officers were hit by birdshot pellets in the Shi'ite village of Karzakan late on Friday, the authority added, quoting Al-Hassan.-Reuters