In addition to the unrest in Daraa - the city where the uprising began more than five weeks ago - security forces were conducting sweeping arrests and raids elsewhere in the country, witnesses said.

Gunfire and sporadic explosions were heard in a tense southern city on Wednesday after the Syrian army sent in more tanks and reinforcements as part of a widening crackdown on the uprising against President Bashar Assad’s authoritarian regime.

In addition to the unrest in Daraa - the city where the uprising began more than five weeks ago - security forces were conducting sweeping arrests and raids elsewhere in the country, witnesses said.

The crackdown came as opposition figures said their “massive grassroots revolution” will break the regime unless Mr. Assad leads a transition to democracy.

The statement from an umbrella group of opposition activists in Syria and abroad called the National Initiative for Change said a democratic transition will “safeguard the nation from falling into a period of violence, chaos and civil war.”

“If the Syrian president does not wish to be recorded in history as a leader of this transition period, there is no alternative left for Syrians except to move forward along the same path as did the Tunisians, Egyptians and Libyans before them,” the statement said.

But the relentless government throttling of the protest movement showed no signed of letting up.

A vigorous crackdown since mid—March has killed more than 400 people across Syria, with 120 dead just over the weekend. Yet the repression has only emboldened protesters who started their revolt with calls for modest reforms but are now increasingly demanding Assad’s downfall.

Mustafa Osso, who cited eyewitnesses on the ground in the city Daraa, said new troops arrived early Wednesday from military bases in the area. Another rights activist, Ammar Qurabi, said security and armed forces have detained more than 400 people in Daraa since a major operation began in the city two days ago.

The opposition is getting more organized as the uprising gains momentum, but it is still largely a grassroots operation. There are no credible opposition leaders who have risen to the level of being considered as a possible successor to Mr. Assad.

The army sent tanks into Daraa, 80 miles (130 kilometers) south of Damascus, on Monday and there have been reports of shooting and raids there and in areas across the country ever since. Daraa is where the uprising began last month.

On Wednesday, witnesses and human rights activists said the army also deployed tanks around the Damascus suburb of Douma and the coastal city of Banias, where there have been large demonstrations in recent weeks.

One Douma resident said security agents were going house—to—house, carrying lists of wanted people and conducting raids. If the agents did not find the person they were looking for, they took his relatives into custody, the resident said.

Two funerals were planned on Wednesday, he said.

In Banias, a witness said the army redeployed tanks and armoured personnel carriers near the main highway leading into the city.

In the coastal city of Latakia, an activist said security forces fired live bullets and stun grenade at demonstrators in poor areas near the city’s Palestinian refugee camp of al—Ramel. He said four people were wounded and several others detained.

Residents contacted by the AP spoke on condition of anonymity out of fear for their safety.

Syria has banned nearly all foreign media and restricted access to trouble spots since the uprising began, making it almost impossible to verify the dramatic events shaking one of the most authoritarian regimes in the Arab world.

Amnesty International said the UN Security Council must refer the situation in Syria to the International Criminal Court.

“The Syrian government is clearly trying to shatter the will of those peacefully expressing dissent by shelling them, firing on them and locking them up,” said Salil Shetty, Amnesty International’s Secretary General.

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