BEIRUT - Syrian security forces opened fire Monday in a restive central city, injuring an Olympic boxing champion and at least 20 others as President Bashar Assad's regime swept through several cities and towns to crush a pro-democracy uprising, activists said.

Nasser al-Shami, who won a bronze medal in the 2004 Olympics in Athens, was in stable condition after being hit by shotgun pellets in the city of Hama, said Rami Abdul-Rahman, the London-based director of the Syrian Observatory for Human Rights. Abdul-Rahman said he spoke to the doctor who treated the athlete.

Monday's shooting happened as Syrian troops and tanks sealed off Hama and blocked the roads leading in, an apparent attempt to crush growing dissent there and retake the city one month after security forces withdrew. About 300,000 protesters held huge protests against the regime in Hama last week, a sign the city was spiraling out of government control.

"There is some kind of a siege on the city. They are closing all roads leading to Hama," said Syria-based rights activist Mustafa Osso.

Hama, which has a history of militancy against the Assad regime, was targeted in a major government crackdown nearly three decades ago. In 1982, Assad's late father and predecessor, Hafez Assad, ordered his troops to crush a rebellion by Sunni fundamentalists, killing between 10,000 and 25,000 people, rights groups say.

Also Monday, activists said Syrian security forces opened fire on people fleeing to neighbouring Turkey, wounding a mother and her young son.

Omar Idilbi, a spokesman for the Local Coordination Committees, which track the protests in Syria, said the shots were fired in Idlib province, near the Turkish border. About 60 people made it across, but authorities detained several others, he said, citing witnesses on the ground.

Thousands of Syrians have already taken shelter in refugee camps in Turkey, a source of deep embarrassment to Damascus.

To the south, in the Damascus suburb of Dumair, armoured personnel carriers rolled in after all telecommunications were cut, an activist in the area said.

The activist, who spoke on condition of anonymity for fear of reprisals, said soldiers and plainclothes policemen were randomly detaining all men from teenagers to people in their 60s.

"There isn't a street in the area without a checkpoint. An ugly detention campaign is ongoing," said the man, who said he counted 27 tanks stationed around Dumair.

The uprising against Assad has proved remarkably resilient, lasting nearly four months despite a deadly government crackdown that has brought international condemnation and sanctions. Assad is facing the most serious challenge to his family's four decades of rule in Syria.

Activists say security forces have killed more than 1,400 people -- most of them unarmed protesters -- since mid-March. The regime disputes the toll, blaming "armed thugs" and foreign conspirators for the unrest.

Syria has banned nearly all foreign media and restricted media coverage, making it nearly impossible to independently verify events on the ground. But witness accounts, including interviews with refugees who have fled to neighbouring countries, indicate a brutal crackdown on the protest movement.

Monday's military manoeuvrs in Hama appeared to be an attempt to reassert government control on the city. The streets had been under the sway of the opposition since June 3, when the army killed more than 60 people in one of the bloodiest days of the uprising, activists said.

On Saturday, Assad fired Hama's governor, Ahmed Abdul-Aziz.

Syria's state-run news agency hasn't said why the governor was dismissed. But some activists said they feared Abdul-Aziz, viewed as sympathetic to the demonstrators, was dismissed to give freer rein to the security forces in the city.

A video posted on a Facebook page run by activists showed that most of the shops were closed in Hama to protest the army's campaign. The five-minute video showed activists driving from one street to another with shops closed as they gave the name of the city and the date.

Another video showed people placing a banner that reads "We wanted to be treated as humans, but they killed us."