Deadly clashes have erupted between Houthi fighters and tribesmen in the city of Baida, several hours after thousands marched in the country's capital, Sanaa, in support of the Houthis who captured the city last year.

The number of casualties was still unclear, but security sources told Al Jazeera that several people had died in the late night violence in Baida on Friday.

Earlier on Friday, Houthi-aligned demonstrators denounced alleged "foreign conspiracies" - a reference to international backing for Yemen's embattled president, who managed to escape house arrest by the rebels earlier this month.

Meanwhile, rallies against the rebels known as Houthis took place in several other places across the country, including cities of Taiz, Hodida and Dhamar.

The rival rallies underscored the depth of the crisis that has gripped Yemen after the Houthis overran Sanaa last September and declared in January that they have taken over the country.

President Abd-Rabbu Mansour Hadi, who managed to escape Sanaa and house arrest by the rebels has established a base in the southern city of Aden.

'No security without unity'

The international community has backed Hadi, and the UN envoy to the country is trying to negotiate a solution to the crisis, including relocating peace talks to outside of Sanaa.

On Thursday, the Houthi rebel leader, Abdel-Malik al-Houthi, claimed Saudi Arabia and other international powers are pushing for a division of Yemen along regional and sectarian lines.

Hadi insists on keeping the country together. "Yemen will not have security without its unity," he told Aden TV on Friday.

Western and Arab countries have shut their embassies in Sanaa, with some relocating to Aden in a sign of support for Hadi.

On Friday, the United Arab Emirates opened its mission on Aden, according to UAE minister of state for foreign affairs, Anwar bin Mohammed Gargash.

Yemen's deepening turmoil, with its threat of full-blown sectarian warfare between Shias, who make up a third of the population and reside mostly in the country's north, and Sunni tribes in the south, has appeared to benefit al-Qaeda's Yemeni branch.

'Great concern' 

Al-Qaeda has targeted both the Houthis on one side, and Yemeni officials and government troops on the other side.

On Thursday night, al-Qaeda fighters ambushed a military truck during a night-time attack in the southern province of Lahj, killing all four soldiers in the vehicle.

Yemeni security officials, speaking on condition of anonymity because they were not authorised to talk to reporters, said the attackers surprised the soldiers with heavy gunfire.

Al-Qaeda in the Arabian Peninsula, as the Yemeni branch is officially known, claimed responsibility in a statement posted one of its Twitter accounts.

It said the fighters set fire to the army truck after they seized the soldiers' machineguns.

Also Friday, a spokeswoman for the UN High Commissioner for Human Rights said the critical conditions in Yemen were being closely monitored with great concern as the political dialogue was faltering.

In Geneva, Ravina Shamdasani said the UN organisation has documented a number of unlawful arrests, arbitrary detentions and targeting of journalists recently.

"It is crucial that all sides exercise restraint and work to resolve the political impasse in a peaceful manner and to avoid the situation from spiraling out of control," Shamdasani said.

Source: Al Jazeera and agencies