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At least two people have been killed and more than 300 injured after Yemen security forces stormed a protest site where thousands of pro-democracy demonstrators have been camped out for weeks, demanding the ouster of the country's leader.

In a pre-dawn raid on Saturday, police are said to have used tear gas and hot water mixed with gas to disperse the demonstrators.

Meanwhile, a teenage boy was killed in separate clashes between security forces and protesters in the city of Mukala.

Al Jazeera's Hashem Ahelbarra, reporting from the capital Sanaa, said that the situation remains tense, and that the opposition is accusing the government of committing crimes against the protesters.

"They also say the raid will speed up the revolution, and that president Ali Abdullah Saleh must go now before [he] faces the wrath of the people," he said.

Also on Saturday, at least three students were injured when security forces opened fire at protesters in the city of Taiz, where residents had gathered to demand that Saleh be put on trial.

The clashes come after tens of thousands of protesters marched on the streets of the capital on Friday, drawing record crowds in a continuing push to demand the ouster of Saleh, who has been in power since 1978.

Thousands of Saleh loyalists also crammed the capital's Tahrir Square, carrying pictures of the veteran leader.

Soldiers killed

Protests, however, turned violent in the southern port city of Aden, where three people were wounded by gunfire and six overcome by tear gas as police tried to disperse the crowd.

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Unidentified armed men on Friday killed four soldiers on patrol east of Mukalla city in Hadhramaut province, in southeast Yemen.

Security sources accused al-Qaeda operatives of being behind the attack. 

A wave of unrest has weakened Saleh's decades-long grip on his impoverished nation, with about 30 people killed since January. 

The protests are part of a wave of popular unrest sweeping across the Arab world, where two presidents in Tunisia and Egypt have been forced to step down.

Meanwhile, a senior White House aide told Saleh on Friday that the United States, which provides substantial financial aid to Yemen, welcomed his steps to resolve the political crisis and urged opposition groups to heed calls for talks.

"All sectors of the Yemeni opposition should respond constructively to president Saleh's call to engage in a serious dialogue to end the current impasse," John Brennan, the senior counterterrorism adviser, told Saleh in a telephone call, the White House said in a statement.

"Brennan noted that the government and the opposition share responsibility for achieving a peaceful resolution of the crisis.

"He also stated that a commitment by all sides to participate in an open and transparent process that addresses the legitimate concerns of the Yemeni people provides an orderly path to a stronger and more prosperous nation."

Saleh's offer rebuffed

On Thursday, Saleh bowed to pressure after a month of violent protests, pledging to devolve power to parliament and to ensure the safety of anti-government protesters. But the opposition rejected the offer saying it came too late.

Saleh said he would hold a "referendum before the end of the year on a new constitution clearly stipulating the separation of powers" between the president and the parliament.

The new charter would "install a parliamentary regime giving all executive powers to a government elected by parliament," he added.

Yemen is a crucial partner of the United States in the fight against al-Qaeda in the Arabian Peninsula (AQAP), which has plotted attacks against US targets from its bases in the country's tribal regions.

It is also battling sectarian and secessionist violence, which have undermined stability and development in one of the poorest countries in the region.

Source: Al Jazeera and agencies