At least 50 people have been killed in two days of fighting between Houthi rebels and government-allied forces at the outskirts of the Yemeni capital, sources tell Al Jazeera.

The army on Wednesday shelled Houthi positions in the suburb of Wadi Dhahr and the Shamlan area, north of the city.

Violence has escalated in recent days, as the government backed by Sunni tribesmen step up their battle against the Shia rebel group.

The upsurge in fighting follows weeks of anti-government demonstrations in Sanaa by Houthi activists calling on the government to resign.

The latest bout of violence started after the rebels set up a new protest camp on Monday close to an army barracks in Hamdan, where Shamlan is located.

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A day later, clashes erupted when Houthis moved into Wadi Dhahr and were confronted by residents.

The army then sent a unit to try to restore order, leading to further clashes with Houthi fighters as troops were ambushed. Many residents in the area fled their homes to escape violence.

Local sources said the rebels had bombed several buildings belonging to the al-Islah party, including the residence of a local leader and a Sunni religious school.

Negotiations ongoing

The Houthis, who follow the small Zaidi branch of Shia Islam, have been embroiled in a decade-old conflict with the central government in Sunni-dominated Sanaa, fighting for more territory and control in the north.

On Monday, the Houthis said they had suspended their participation in negotiations with the Yemeni government about a solution to their grievances because of what they termed "foreign interventions" in the course of the discussions.

But on Wednesday, UN top envoy to Yemen Jamal Benomar travelled to Saada in the north of the country for talks with Houthi leader Abdul Malek al-Houthi.

"We're hearing from UN sources that it's unlikely they'll sign a landmark deal later today but it's the first-time a high-level delegation went to Saada," Al Jazeera's Hashem Ahelbarra, reporting from Sanaa, said.

The talks aim to end a crisis that has seen weeks of sometimes bloody protests in Sanaa, where Houthi protesters have been blocking the main road to the international airport and holding sit-ins at ministries to try to oust the government and restore fuel subsidies cut by the state in July as part of economic reforms.