Bahraini security forces raided the house of top Shi'ite cleric Ayatollah Sheikh Isa Qassim on Friday, the opposition said, an act likely to enrage the island's majority Shi'ite population which is at loggerheads with its Sunni rulers.
Bahrain, where the US Fifth Fleet has its base on Iran's doorstep, has been in violent turmoil since Shi'ite-led pro-democracy protests erupted in 2011.
Protests continue and often end in clashes between demonstrators and police. At least two people have died this year.
Security personnel forced open the door of Sheikh Isa's home in the village of Duraz in the early hours of Friday morning and searched the house, Bahrain's main opposition bloc al-Wefaq said on its website.
Women and children from the sheikh's family were in the house at the time of the raid, but the sheikh was not at home, al-Wefaq said. Noone was reported hurt.
In a statement to state media, Bahrain's chief of public security made no mention of the raid but said police on duty in Duraz early on Friday had come under fire from a "locally made weapon", injuring two officers.
In response, "necessary measures were taken to reinforce the security force patrols with members of an anti-terrorism unit ... to uncover the source of the gunfire," Major-General Tariq Al-Hassan told the state news agency BNA.
He said the shooting was still under investigation.
A leading Bahrain human rights activist said he believed security forces had entered the sheikh's house in pursuit of fugitives who had fled there from a neighbouring house.
"This is the first time (his house was raided) and it's hugely offensive for a huge number of Shi'ites in Bahrain," said Mohammed al-Maskati, president of the Bahrain Youth Society for Human Rights.
"People see him as a red line. I expect that this will cause a big reaction."