Pro-democracy protests which swept the Arab world earlier in the year have erupted in eastern Saudi Arabia over the past three days, with police opening fire with live rounds and many people injured, opposition activists say.

Saudi Arabia last night confirmed there had been fighting in the region and that 11 security personnel and three civilians had been injured in al-Qatif, a large Shia city on the coast of Saudi Arabia's oil-rich Eastern Province. The opposition say that 24 men and three women were wounded on Monday night and taken to al-Qatif hospital.

The Independent has been given exclusive details of how the protests developed by local activists. They say unrest began on Sunday in al-Awamiyah, a Shia town of about 25,000 people, when Saudi security forces arrested a 60-year-old man to force his son – an activist – to give himself up.

Ahmad Al-Rayah, a spokesman for the Society for Development and Change, which is based in the area, said that most of the civilians hit were wounded in heavy firing by the security forces after 8pm on Monday. "A crowd was throwing stones at a police station and when a local human rights activist named Fadel al-Mansaf went into the station to talk to them and was arrested," he said.

Mr Rayah added that "there have been protests for democracy and civil rights since February, but in the past the police fired into the air. This is the first time they have fired live rounds directly into a crowd." He could not confirm if anybody had been killed.

The Shia of Saudi Arabia, mostly concentrated in the Eastern Province, have long complained of discrimination against them by the fundamentalist Sunni Saudi monarchy. The Wahhabi variant of Islam, the dominant faith in Saudi Arabia, holds Shia to be heretics who are not real Muslims.

The US, as the main ally of Saudi Arabia, is likely to be alarmed by the spread of pro-democracy protests to the Kingdom and particularly to that part of it which contains the largest oil reserves in the world. The Saudi Shia have been angered at the crushing of the pro-democracy movement in Bahrain since March, with many protesters jailed, tortured or killed, according Western human rights organisations.

Hamza al-Hassan, an opponent of the Saudi government from Eastern Province living in Britain, predicted that protests would spread to more cities. "I am frightened when I see video film of events because most people in this region have guns brought in over the years from Iraq and Yemen and will use them [against government security men]," he said. He gave a slightly different account of the start of the riots in al-Awamiyah, saying that two elderly men had been arrested by the security forces, one of whom had a heart attack.

"Since September there has been a huge presence of Saudi security forces in al-Qatif and all other Shia centres," he said. Al-Qatif was the scene of similar protests in March, which were swiftly quashed by security forces.

The Saudi statement alleges that the recent protests were stirred up by an unnamed foreign power, by which it invariably means Iran. The interior ministry was quoted on Saudi television as saying that "a foreign country is trying to undermine national security by inciting strife in al-Qatif". Saudi Arabia and the Sunni monarchies of the western Gulf have traditionally blamed Iran for any unrest by local Shia, but have never produced any evidence other than to point at sympathetic treatment of the demonstrations on Iranian television.

The 20 doctors in Bahrain sentenced to up to 15 years in prison last week say their interrogators tortured them repeatedly to force them to make false confessions that Iran was behind the protests. The counter-revolution in Bahrain was heralded by the arrival of a 1,500-strong Saudi-led military force, which is still there.

Mr Rayah, who flew from Saudi Arabia to Beirut to be free to talk about the protests, said: "People want a change and a new way of living." He said that, in particular, they were demanding a constitution and a free assembly for the Eastern Province. He also wanted the Society for Development and Change legally registered.

Mr Hassan blamed the protests on the fact "that there has been no political breakthrough".

"I am from the city of al-Safwa, which is very close to al-Awamiyah, and there is very high unemployment in both," he said. Some 70 per cent of the Saudi population is believed to be under 30 and many do not have jobs. "We were hoping for municipal reforms and regional elections for years but we got nothing."