A pro-reform protester throws back a gas bomb fired by police during clashes on the outskirts of Manama, Bahrain, on Monday. Injuries were reported among protesters and police ranks, before police managed to turn away the protesters.

MANAMA -- Security forces in Bahrain fired tear gas and stun grenades at protesters trying to occupy a landmark square in the nation's capital on Monday ahead of the one-year anniversary of the Gulf kingdom's Shiite-led uprising.

Traffic came to a standstill on the highway, the main thoroughfare into the capital of the regional banking hub.

"We will not back down," said Nader Abdulimam, who had taken refuge in a house just outside of Manama with other protesters overcome by tear gas. "This has gone on for one year and it will go for another year or more."

Opposition supporters were undeterred by the authorities' warnings of zero tolerance for anti-government activities around the strategic island that is the home of the U.S. Navy's 5th Fleet.

Sheikh Ali Salman, leader of the largest Shiite opposition group Wefaq, had earlier called on youths to eschew violence in protests after clashes with police escalated in recent weeks, with teenagers throwing bombs and iron bars.

In an area about six miles west of central Manama, some demonstrators stood atop Bahrain's ancient burial mounds — some more than 5,000 years old — waving flags featuring the image of Pearl Square's six-pronged monument.

Inspired by uprisings in Egypt and Tunisia, Bahrainis -- mainly from the Shiite majority -- took to the streets on February 14, 2011, to demand democratic reforms. But the Sunni Muslim-led government crushed the protests a month later after talks involving Wefaq went nowhere and sectarian violence spread.

'Just a case of manners'
Mainly Shiite opposition parties are demanding Bahrain's elected parliament be given the power to form governments. Shiites complain of political and economic marginalization by an entrenched elite who do not want to share power.

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

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In an interview with Germany's Der Spiegel magazine, King Hamad 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. Reuters journalists have not witnessed the opposition chanting in support of Khomeini.

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"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."

Human rights organizations say that the government is not doing enough to deal with the demands of protesters.

The Associated Press and Reuters contributed to this report.