Rebel forces and loyalist fighters were locked in fierce fighting in Yemen Monday as hopes of a political solution faded after the United Nations postponed peace talks.
Clashes raged in the country's third city Taez, sowing panic after Shiite Houthi rebels bombarded several districts with rocket and tank fire.
"There's a real massacre going on in Taez, the city that spearheaded the revolt" against former president Ali Abdullah Saleh who now supports the Houthis, one resident said.
"Saleh has aligned himself with the rebels to take revenge," Bassam al-Qadhi added.
Saleh quit in early 2012 after bloody, year-long protests against his rule, and was replaced by Abedrabbo Mansour Hadi who has taken refuge along with his government in neighbouring Saudi Arabia.
Monday's clashes in Taez came just four days before a new UN effort was to have been held, aiming to resolve the conflict in the impoverished Arabian Peninsula nation.
However, there had been growing uncertainty over which of the warring parties would attend the talks slated for Thursday in Geneva.
"I can confirm that the meeting has been postponed," a UN official told AFP, without elaborating.
The postponement is another blow to UN efforts to broker peace in a country where nearly 2,000 people have been killed since March.
Hadi had laid out his government's demands in a pre-talks letter to the UN secretary general Ban Ki-moon, insisting that the rebels must withdraw from the territories they have seized.
He reiterated his position during talks in Riyadh with Ban's special envoy Ismail Ould Cheikh Ahmed.
In a bid to restore Hadi's authority, Saudi Arabia has led an air campaign against the Houthis since March 26.
Coalition aircraft bombarded targets across the country on the weekend, including the airport in second city Aden and its northern suburbs, officials said.
The clashes, which erupted Sunday and raged overnight, have killed at least 30 Houthi rebels and allied forces, the official told AFP.
He said a provisional toll showed at least five Hadi loyalists were also killed.
For a second consecutive day, rebels and their allies targeted several Taez neighbourhoods with rockets and tank shells, residents said.