BEIRUT - Syrian troops opened fire on people throwing stones to stop a convoy from advancing toward an eastern oil hub, killing as many as three people Saturday, activists said, as government forces intensified a pre-Ramadan crackdown against protests calling for President Bashar Assad's ouster.

Activists have predicted that demonstrations will escalate during the Islamic holy month, which begins Monday, as both sides try to tip the balance in the more than four-month uprising.

During Ramadan, Muslims throng mosques for special night prayers after breaking their dawn-to-dusk fast every day. Such gatherings could trigger intense protests throughout the predominantly Sunni country and activists say authorities are moving to ensure that doesn't happen.

Syria-based rights activist Mustafa Osso said the regime has detained more than 4,000 people in raids over the past week as it tries to contain the situation.

"The regime is trying to suppress the uprising because it knows that the opposition will try to hold protests between sunset and sunrise," Osso said. He called the week of raids the "strongest security campaign since the uprising began."

On Saturday, government forces stormed parts of the eastern city of Deir el-Zour and barraged neighbourhoods with heavy machine-gun fire, two days after army defectors fought with Assad loyalists, activists said.

An activist in Deir el-Zour said the attack began in the afternoon and that one person was shot dead in a nearby village. Rami Abdul-Rahman, the director of the London-based Syrian Observatory for Human Rights, said about 60 vehicles filled with reinforcements from the northern city of Raqqah reached Deir el-Zour after noon.

Abdul-Rahman gave a higher death toll, saying troops shot dead three people in the nearby village of Tibni when they tried to stop advancing troops by throwing stones.

"Intense shooting could be heard in the western parts of the city," he told The Associated Press by telephone. "Residents have placed barriers in the streets in order to obstruct advancing troops."

Deir el-Zour, the capital of a province that carries the same name, is an oil hub but one of the country's poorest regions. The tribal region, which borders Iraq, has been witnessing intense protests calling for the downfall of Assad's regime.

Authorities have waged a brutal crackdown nationwide that activists say has killed more than 1,600 civilians since the protests against the regime began in mid-March. The government has sought to discredit those behind the protests by saying they are terrorists and foreign extremists, rather than true reform-seekers.

Since the uprising against Assad's regime began in mid-March, Fridays have witnessed the most intense protests as Muslims leave mosques after the weekly prayers and march in the streets demanding Assad's downfall. Mosques have become gathering points as it is almost impossible for activists to get a license from the government for anti-regime gatherings.

The Deir el-Zour raid followed a nighttime attack by government forces on the capital of Damascus and the eastern city of al-Boukamal on the border with Iraq.

Last week, Assad fired and replaced the governor of Deir el-Zour after massive anti-government demonstrations in the area. Activists say Samir al-Sheik, who was a Damascus-based police brigadier general, was chosen to try to put an end to protests in the region.

Activists said scores of people also were detained elsewhere in Syria Saturday, most in the eastern town of al-Boukamal, the northern province of Idlib and some Damascus suburbs.

Also Saturday, Lebanese security officials said Syrian troops opened fire at about 50 families fleeing the crackdown into northern Lebanon. The officials, who spoke on condition of anonymity in line with regulations, said no one was hurt and the families entered the Lebanese village of Knayseh.

The Syrian observatory said four people were killed during a raid on the Damascus suburb of Kiswah Friday night. It also said that one person was killed when troops entered al-Boukamal. Those deaths raised the total death toll on Friday to 12, according to the human rights group.

Mohammed Abdullah, a spokesman for the Local Coordination Committees, which track the protests in Syria, said at least six people were killed in the Kiswah raid, and he gave a total death toll of 22 for Friday.

Ammar Qurabi, who heads the National Organization for Human Rights in Syria, said 19 people were killed on Friday, including three in Kiswah and two in al-Boukamal.

It was not clear why the numbers were different but each group is known to have its own sources throughout Syria.

The observatory, which is known to be more conservative in its estimates, said Saturday that 1,888 people have been killed since the uprising began, including 1,519 civilians. It said the rest were members of the military and security forces.

Other groups such as Qurabi's NOHRS and the LCC put the death toll among civilian well above 1,600.

The uprising has been the most serious threat to the 40-year ruling dynasty of the Assad family.

Assad, who inherited power in 2000 after the death of his father, President Hafez Assad, has made a series of overtures to try to ease the growing outrage. He lifted the decades-old emergency laws that gave the regime a free hand to arrest people without charge, granted Syrian nationality to thousands of Kurds -- a long-ostracized minority -- and issued several pardons.