Suspected al-Qaeda gunmen killed six soldiers, including two officers, in three separate attacks Sunday in several restive regions of the country, officials said.
Meanwhile, Yemen's opposition movement vowed today to intensify protests against the regime of President Ali Abdullah Saleh, after the embattled leader refused to resign by the end of the year.
With violence gripping the strategic US ally on multiple fronts, the United States and Britain advised citizens to consider leaving the Arabian peninsula nation and warned against all but essential travel.
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 February 16, according to an AFP toll.
"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.
Yemen is a key US ally in the war against Al-Qaeda in the Arabian Peninsula (AQAP), which has plotted several foiled attacks against the United States.
The bloodshed comes amid mounting protests against the regime of President Ali Abdullah Saleh, who claims to be the guarantor of security in the deeply tribal and impoverished country.
Unidentified gunmen believed to be from Al-Qaeda shot dead four soldiers from Yemen's elite Republican Guard near Marib, about 170 kilometres (110 miles) 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.
Colonel 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, requesting anonymity.
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 Colonel 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.
A US State Department official last month described Yemen-based AQAP -- a fusion of the Yemeni and Saudi branches of the jihadist network -- as the "most significant" threat to the US homeland.