The Yemeni police's attempt to clear out anti-government protesters by force may undermine the reconciliation between the ruling party and opposition, which could reach a stalemate over the political crisis of the country, analysts said.

Massive demonstrations rattled Yemen's major cities on Saturday after police stormed a sit-in of nearly 100,000 protesters outside Sanaa University in the capital at dawn, leaving at least four protesters dead and over 300 others injured.

The opposition coalition then called for people to take to the streets and join anti-government protest in a statement obtained by Xinhua.

The opposition also held Yemeni President Ali Abdullah Saleh responsible for Saturday's storm against the demonstrators, describing the attack as "massacre."

"We reaffirm our unchangeable stance that we stand with our people's volition and rights to live freely," they said in the statement.

Local analyst Saif Hassan, the head of Sanaa-based Yemeni Political Forum, said the police's attack against the protesters has aggravated further the deadlock between the ruling party and opposition.

"The attack closed the door of the possible reconciliation and opened another for the regime to leave," Hassan told Xinhua.

"The conciliation between the ruling party and the opposition seems ended after both sides turned to violent confrontation," Hassan said, adding "the crisis now moves into street. It seems that it is the time for opposition to take decisive action."

Foad al-Salahi, a professor of Political Sociology of Sanaa University, said the violence by police made the protesters more unified.

"Some forces within the state security agencies seek to exacerbate the situation in order to justify the use of arms against protesters, but the opposition, tribes and protesters are aware of such plots," al-Salahi told Xinhua.

"What happened near Sanaa University on Saturday clearly showed the intention of both sides," he suggested, "the Yemeni public is sending an unified message for the first time that people want to topple the regime, especially after many powerful tribes joined the rows of protesters, which could speed up the downfall process. "

At least four protesters were killed by police gunshot on Saturday in Sanaa and a schoolboy was shot dead in the southern city of Mukalla, while a 20-year-old demonstrator died of gunshot wound in a hospital in the southern Taiz province, according to witnesses and security sources.

Twfic al-Yazidy, an architect at the scene of protest in Sanaa, told Xinhua that "the police using live bullets and tear gas failed to break up the rally as protesters managed to repel the attack, and keep shouting 'we are peaceful'."

Electricity was cut off as streets leading to the scene were blocked after the police put the sit-in under a tightened siege.

Another hundreds of protesters were injured in the demonstrations across the country's major provinces, said doctors and eyewitnesses.

However, spokesman of Yemen's ruling party Yaser al-Yamany denied that the protesters were killed by police gunshot, telling Xinhua that the police were trying to protect the sit-in after a numbers of armed protesters clashed with some house owners near the sit-in over disputes.

"Owners of the houses near the sit-in complained that they were annoyed and attacked by protesters," al-Yamany said, adding that police officials and local councilmen are investigating into the event.

Inspired by Tunisian and Egyptian protests, protesters in Yemen staged daily rallies since mid February, calling for Saleh's resignation.

On Thursday, Saleh offered the opposition a fresh reform initiative, which said to transfer power to the parliament by the end of this year but was swiftly rejected by the opposition.