|Yemeni anti-government protesters have been calling for the ouster of the country's president [AFP]
Five Yemeni soldiers have been shot dead in two separate suspected al-Qaeda attacks as protests continued Sunday against the decades-old rule of Ali Abdullah Saleh, the country's president.
Four Yemeni soldiers were killed in the province of Marib, to the east of the capital, Sanaa, when attackers opened fire on the soldiers as they passed in a military vehicle on Sunday, sources told Al Jazeera.
The soldiers were members of the country's elite Republican Guard, according to the AFP news agency.
"The attack was similar to others by al-Qaeda," a Yemeni official told AFP. A military attack helicopter and ground troops pursued the assailants into a nearby valley, a security source said.
Meanwhile, an army colonel was shot dead as he shopped in Zinjibar, capital of the southern Abyan province. Al-Qaeda fighters have mounted a series of deadly attacks on military targets since the beginning of the year.
Opposition leaders on Sunday called for intensified demonstrations as Yemeni government loyalists were reported to have attacked anti-government protesters in the town of Ibb, south of Sanaa.
At least 40 pro-democracy protesters were injured in clashes, local sources told Al Jazeera. Gunfire was heard and loyalists used stones and batons. Six people were in a critical condition, the Reuters news agency reported.
At least 19 people have been killed since the protests began on February 16, according to an AFP toll based on reports and witnesses. Human rights group Amnesty International has put the toll at 27.
"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," Mohammed Sabri, an opposition leader, told AFP.
Saleh, in power since 1978, on Saturday rejected calls for him to step down by the end of the year and vowed to stay in power until 2013.
In a statement carried late Saturday on the state-run Saba news agency, an official close to the president said the opposition's proposal, envisaging Saleh's departure before the end of the year, was "vague and contradictory".
"A peaceful transition of power cannot be done with chaos, but by having recourse to the people through elections, so that they can decide who they want to lead without acts of violence and trouble," the statement said.
Saleh on Sunday spoke to Sultan Qaboos bin Said, the leader of neighbouring Oman which has also been rocked by anti-government unrest, to discuss developments in the region, Saba reported.
The US government has warned Americans against travelling to Yemen and authorised the voluntary departure from the country of family members and non-essential embassy staff.
"The department [of state] urges US citizens not to travel to Yemen. US citizens currently in Yemen should consider departing Yemen," the US state department said in a travel warning on Sunday.
"The security threat level in Yemen is extremely high due to terrorist activities and civil unrest."
A US state department official last month described the Yemen-based al-Qaeda in the Arabian Peninsula - a fusion of the Yemeni and Saudi branches of the network - as the "most significant" threat to the US homeland.
Britain advised its nationals against all travel to Yemen on Saturday.