Bahrain's King Hamad has banned protests in Manama in an amendment to a law on public gatherings, ahead of a major opposition demonstration called for mid-August, state news agency BNA reported.

The monarch, whose kingdom has been rocked by Shiite-led protests since 2011, also toughened penalties against the guardians of minors caught taking part in protests, BNA said late on Tuesday.

The Bahraini authorities have arrested three suspects linked to a car bomb that exploded outside a Sunni mosque south of the capital Manama, the government said on Sunday.

"Three people suspected of involvement in the terrorist act that took place near Sheikh Isa bin Salman mosque in Rifaa have been arrested," the interior ministry said on its Twitter account.

Bahraini security forces clashed with anti-regime protesters early Friday, leaving several people wounded including a policeman who was shot with a home-made gun, the interior ministry and witnesses said.

Hundreds took part in protests that erupted late Thursday and lasted until the early hours of Friday across several Shiite villages after a call was issued by the opposition February 14 Coalition youth group, witnesses and activists said.

Unknown assailants have hurled petrol bombs at Bahrain's foreign ministry in the first attack on a government building in more than two years of unrest, the interior ministry said on Tuesday.

"A group of terrorists attempted to attack the Dar al-Hukumah compound with petrol bombs," the ministry said on its Twitter account, adding that guards repelled them and that there was no damage caused in the late Monday attack.

Thousands of Shiites demonstrated near Manama on Saturday in a new protest against an appeals court upholding jail terms for 13 activists on charges of plotting to overthrow Bahrain's monarchy, witnesses said.

"We will not resign ourselves to it" and "we will not forget the prisoners," shouted demonstrators during the peaceful protest that was monitored by a heavy security presence. Some carried photos of those convicted.

A fire in a three-storey block housing Asian workers in the Bahraini capital killed at least 13 people, the state BNA news agency reported late on Friday.

One firefighter was also injured when the building's roof collapsed during a rescue attempt, the news agency added.

Bahrain said Sunday it has reinstated its ambassador in Iran, more than a year after recalling the envoy over Tehran's strong condemnation of Manama's brutal crackdown on Shiite-led protests.

"The ambassador of the kingdom to the Islamic Republic of Iran has returned to his work in Tehran," announced Foreign Minister Sheikh Khaled bin Ahmed Al-Khalifa on his Twitter page.

Bahrain's appeals court on Thursday acquitted nine medics and cut the jail terms of nine others for their role in anti-regime protests last year, in a case which drew widespread criticism from rights groups.

The 20 doctors and nurses in the case worked at Manama's Salmaniya Medical complex, stormed by security forces after a crackdown on a protest encampment at the capital's nearby Pearl Square in March 2011.

Bahraini police wounded several people on Saturday morning when they fired sound bombs, tear gas and bird shot to disperse dozens who protested across several Shiite areas, witnesses said.

"Down Hamad," chanted dozens of supporters of the youth group of the "Revolution of February 14," referring to Bahrain's Sunni monarch. "The people want to overthrow the regime."

Saudi tycoon Prince Alwaleed bin Talal has signed agreements with Bahrain to move his Rotana news and entertainment company from Cairo to the protest-hit Gulf state, the official BNA agency said on Wednesday.

The move comes as Prince Alwaleed plans to launch 24-hour news channel, Alarab in the first half of 2013 to compete with Al-Jazeera, Al-Arabiya and the newly-launched Sky News Arabia satellite news channels.