Bahraini riot police waged pitched battles with petrol-bomb throwing youths on Sunday as violence escalated before the February 14 anniversary of an uprising last year, while King Hamad suggested protesters calling for his overthrow was a 'problem for national unity'.

Teenagers blocked off streets in the village of Sanabis, taunting police as 'cowards' and 'mercenaries' because some are thought to be Pakistani or Yemeni. A policeman shouted to people to get indoors. "This gathering is illegal," he said.

One teenager lobbed four petrol bombs some 30 meters towards a group of police, who responded with a volley of sound grenades and tear gas. Shops were mostly locked up in the district, which was riddled with blocked roads and anti-government graffiti.

Bahrainis, mostly from the Shi'ite Muslim majority, initially took to the streets last February, inspired by uprisings in other Arab states, but the government imposed martial law and stamped out the unrest the following month with the help of Saudi troops.

Demonstrations began again after the emergency law was lifted in June and are escalating before the anniversary of the 2011 protests.

Bahrain is an ally of the United States and home base to the U.S. Navy's vast Fifth Fleet, which patrols the Gulf. It is ruled by a Sunni Muslim royal family, but most of its people are Shi'ites, placing it on the fault line of regional influence between Sunni power Saudi Arabia and Shi'ite Iran.

The ruling Al Khalifa family accuses Iran of fomenting the uprising. Tehran denies playing a role, and Bahrain's Shi'ite groups deny they receive support from abroad.

In an interview with Germany's Der Spiegel magazine, the king accused his opponents of chanting in support of Ayatollah Khomeini, leader of Iran's 1979 revolution.

"It's just a case of manners. But when they shout 'Down with the king and up with Khomeini' that's a problem for national unity," the magazine quoted Hamad as saying in extracts of the interview, the rest of which would be published on Monday.

The refrain 'Down with Hamad', sounded by trumpets and car horns and chanted at rallies, has become a rallying call of opposition protests.

"In a sense there is no 'opposition' in Bahrain, as the phrase implies one unified bloc with the same views," Hamad said in the extracts. "Such a phrase is not in our constitution, unlike say the United Kingdom. We only have people with different views, and that's okay."

Violent Clashes

Opposition actions have involved marches organized by opposition parties with government approval, as well as street protests called by activists online under the title February 14 Youth Coalition, which usually result in clashes with police.

One of the activists, bearing a large rock and masking his face with a scarf, said the clashes were a result of police action against peaceful protests.

"Today we sat outside our homes as a peaceful method of protest. Then the repression by these Khalifa forces began," he said. "So we have to confront them. It was before our houses. They are the ones who came in their cars."

The government says such clashes are acts of hooliganism by youth who put police and other Bahrainis' lives in danger. Police say they must act to restore law and order.

"People have come to the conclusion that the opposition only want to bring unrest to the country. They are not serious about any goals," said Jamal Fakhro, deputy head of the appointed house of parliament.

After last year's demonstrations, the government demolished a sculpture at the Pearl Roundabout, a landmark traffic junction that had been occupied by protesters for a month. Security forces are determined not to let protesters return to the site.

Leading activist Nabeel Rajab led several hundred people in an attempted march to the roundabout on Saturday, which ended with the arrest of two American activists, who were deported on Sunday. Rajab staged a smaller walk to the roundabout with his family on Sunday, reaching the edge of the heavily guarded zone where security forces fired tear gas to disperse the group.

"This is a continuous protest," he said, walking back with his 9-year-old daughter, who appeared distressed from the effects of the tear gas. "There will not be one central protest with thousands of people, it will be all over."

Zainab al-Khawaja, daughter of rights activist Abdulhadi al-Khawaja, one of 14 prominent figures in last year's protests who are in prison, was detained by police for also attempting to walk into the roundabout with a small group of activists.

Mainly Shi'ite opposition parties are demanding Bahrain's elected parliament be given the power to form governments. Shi'ites complain of political and economic marginalisation by an entrenched elite who do not want to share power.

The government denies this and says it is making reforms such as giving an elected chamber more powers of scrutiny over ministers and budgets.

In his interview, Hamad defended last year's martial law, which he said was intended to protect women and expatriates from attack: "Also our women were very scared and it is the duty of a gentleman to protect women, so I had to protect them."

Thirty-five people died by the time martial law ended, including protesters, police, Shi'ite detainees and foreigners. The ongoing clashes have taken the death toll above 60, although the government disputes the causes of death of many.

The king also said he called in Gulf military help, mainly in the form of Saudi troops, to protect Bahrain's "strategic installations... in case Iran would be more aggressive."

Despite dealing firmly with its own protests, Bahrain has been one of the Gulf Arab countries leading the Arab League in opposing Syria's Bashar al-Assad, an ally of Iran. The Arab League voted on Sunday to back the Syrian opposition's uprising against Assad, and to call for U.N. peacekeepers in Syria.

"The best advice for him is from the Syrian people," Spiegel quoted Hamad as saying of Assad.