Four people were killed and several wounded by gunfire in the vicinity of a mosque in Oman, the Omani police said on Tuesday, marking a rare breach of security in one of the most stable countries in the Middle East.

"All security measures and procedures have been taken to deal with the situation, and procedures for gathering evidence and investigation are being completed," the police said in a statement.

The US embassy in the capital Muscat said it is following reports of the shooting incident in Wadi al-Kabir, in the governorate of the capital city Muscat. "US citizens should remain vigilant, monitor local news and heed directions of local authorities," it said in a statement.

Oman has maintained its neutrality in the turbulent region and has mediated in disputes, including those between the United States and Iran.