Police shot dead seven Shiite rebel activists attempting to storm government headquarters Tuesday and troops clashed with rebels on Sanaa's outskirts, amid warnings Yemen is at a "dangerous crossroads."
The violence comes after rebel chief Abdulmalik al-Huthi vowed to step up protests and with Saudi Arabia accusing rebels of "conspiring" to destabilise Yemen.
Activists have been camped out in the capital for weeks in a campaign to bring down the government and secure greater representation in state institutions.
Thousands of the Huthi rebel activists blocked main thoroughfares in central Sanaa Tuesday, with some of them marching on government headquarters, witnesses said.
They were met by anti-riot police who fired live rounds, tear gas and water cannon, "killing seven of them and wounding dozens," activist Khaled al-Madani told AFP.
In a statement on the official Saba news agency, an interior ministry official confirmed that police had stopped protesters, who "tried to storm... the premises of the council of ministers."
AFP could not independently verify the Huthi toll.
Later in the afternoon, troops prevented a Huthi vehicle loaded with arms from entering the capital, sparking a clash in Hiziaz, a southern entrance to Sanaa, a security official said.
An army officer was wounded, the official told AFP.
The protesters also tried unsuccessfully to enter state radio headquarters, the authorities said.
Saba quoted the high commission for security as saying, without giving details, that a number of guards were hit by gunfire from the attackers, and the health ministry said an ambulance driver was killed.
On Sunday, the rebels said two demonstrators were shot dead and around 40 wounded in clashes with police special forces near the interior ministry, where the rebels have been expanding their sit-in and blocking a main road leading to the airport.
Huthi protesters have forced shut the ministries of electricity and telecommunications and rebels on Monday prevented government vehicles from entering or leaving the capital.
Speaking late Monday, the Huthi commander vowed "we will continue our escalation," while saying "negotiations will continue".
So far, the rebel movement has rejected overtures from President Abdrabuh Mansur Hadi in offering a new prime minister and reducing a disputed fuel price hike.
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Both concessions were core demands of the Huthis who launched their protest on August 18, after battling loyalist forces for months for control of key cities north of Sanaa.
- 'Tense situation' -
Yemen has been locked in a protracted transition since long-time president Ali Abdullah Saleh was forced from power in February 2012 after a deadly 11-month uprising.
The International Crisis Group warned Monday that "Yemen's troubled transition is at a crossroads more dangerous than any since 2011."
"The situation is tense," said the Brussels-based think-tank.
Unless an "inclusive settlement" based on Hadi's initiative is reached, the "alternative is a conflict," it said.
"While the Huthis' ambitions are unclear and evolving, the protests are part of a bargaining process through which the movement hopes to become dominant in the north and more powerful on the national level."
Analysts say the rebels are trying to establish themselves as the top political force in the northern highlands bordering Saudi Arabia, where Shiites are the majority.
In a telephone call to Hadi, Saudi Foreign Minister Saud al-Faisal voiced his country's "deep concern over the dangerous escalation by Huthi militias in Sanaa and its surroundings of Jawf and Marib," north and east of Sanaa.
"Yemen's security, stability, and unity are strategically important" to the kingdom, the region, and the international community, Saba quoted Faisal as saying.
"Any attempt to undermine it under whatever excuse reflects a hidden agenda conspiring to destabilise the whole region," said Faisal.
Authorities in Sunni-majority Yemen and Saudi Arabia accuse Shiite-dominated Iran of backing the rebels.
The rebels have been battling the government for years from their Saada heartland, complaining of marginalisation under Saleh, whom Hadi replaced in 2012.
The government's plans for a six-region federation to address the grievances of the regions have been rejected by both the Shiite rebels and southern separatists.