“The Department (of State) urges US citizens not to travel to Yemen. US citizens currently in Yemen should consider departing,” the US State Department said in a travel warning.

“The security threat level in Yemen is extremely high due to terrorist activities and civil unrest.” The growing Yemeni protests, and a series of defections from Saleh’s allies, have added pressure on Saleh to end his three-decade rule. Neither side appears willing to compromise.

“The country is on the brink of imploding,” said Dubai-based security analyst Theodore Karasik. “This popular uprising is going to hit some kind of crescendo and you might have an outbreak of more violence. We might be looking at a Libya situation emerging in Yemen.”

Mohammed Sabri, a leading member of the opposition Common Forum, vowed to step up anti-government demonstrations which have left at least 19 people dead since Feb. 16.

“We have called upon the people to widen demonstrations and escalate the peaceful struggle in all regions until he (Saleh) is left with one option, that is to leave,” he said.

Meanwhile, suspected Al-Qaeda gunmen killed six soldiers, including two officers, in three separate attacks Sunday in several restive regions.

Unidentified gunmen believed to be from Al-Qaeda shot dead four soldiers from Yemen’s elite Republican Guard near Marib, about 170 km east of Sanaa, a local official said.

“The attack was similar to others by Al-Qaeda,” he added.

Al-Qaeda militants shot and killed an army intelligence officer in the city of Zinjibar, in southern Abyan province, a local official said.

Col. Abdulhamid Al-Sharaabi “was in the market when two men riding a motorbike attacked him, with one of them shooting him. He died instantly, while the two men ran away,” the official said.

Another officer was later shot dead in the city of Sayun, in the eastern province of Hadramut, by gunmen suspected to be from Al-Qaeda, a security official said.

Two gunmen on a motorbike gunned down Col. Shayef Al-Shuaibi at a restaurant, witnesses said. Shuaibi was hit in the head and died instantly, they said.

Al-Qaeda militants have regrouped in the southern Arabian Peninsula state, particularly in Marib, Abyan and Hadramut.