* Clashes, gunfire erupts at protest in Ibb, dozens hurt
* Six security men killed in three attacks, al Qaeda blamed
(Adds more violence, British warning, opposition remarks)
By Mohamed Sudam
SANAA, March 6 (Reuters) - The United States warned citizens in Yemen on Sunday to consider departing as protests seeking the ouster of President Ali Abdullah Saleh gather momentum, saying the security risk in the impoverished state was extremely high.
Tens of thousands of protesters have camped out in major Yemeni cities, their tone hardening daily, and protests turned to clashes in the town of Ibb on Sunday when government loyalists attacked demonstrators with sticks and stones.
Violence also flared in outlying provinces, where six security men were killed in attacks blamed on al Qaeda. "The Department (of State) urges U.S. citizens not to travel to Yemen. U.S. citizens currently in Yemen should consider departing," the U.S. State Department said in a travel warning.
"The security threat level in Yemen is extremely high due to terrorist activities and civil unrest," it added. Britain has also warned against travel, advising those without a pressing need to stay to leave by commercial flights. The growing Yemeni protests, and a series of defections from Saleh's allies, have added pressure on Saleh to end his three-decade rule in the Arabian Peninsula state. But neither side appears willing to compromise to end the deadlock.
Protesters want Saleh to step down by the end of this year, if not sooner, while the president is sticking to an earlier pledge to leave office only when his current term ends in 2013. Yemen, a neighbour of Saudi Arabia, was teetering on the brink of failed statehood even before recent protests, with Saleh struggling to cement a truce with Shi'ite rebels in the north and quell a secessionist rebellion in the south.
Analysts say the recent protests, inspired by unrest that has toppled the leaders of Egypt and Tunisia and sparked an insurrection in Libya, may be reaching a point where it will be difficult for Saleh, an astute politician, to cling to power. "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."
Washington said its ability to help citizens in a crisis could be restricted, and evacuation options would be "extremely limited". It authorised the voluntary departure of the family members of U.S. embassy staff and non-essential personnel.
Yemeni protests, relatively peaceful in recent days, turned to violence in the town of Ibb when Saleh loyalists marched on an anti-government protest site in a park where thousands were camped out, attacking demonstrators with stones and batons. "There were a large number who tried to storm the park carrying clubs and pelting us with stones and shouting: 'No to destruction and chaos'," said protester Ahmed Saleh, citing a slogan widely used by Saleh supporters.
Police fired in the air to disperse the protesters. At least 47 people were hurt in the melee, six critically, including a youth protest leader, an activist and witnesses said. Some 26 people have been killed since protests surged in early February. Opposition leader Yassin Said Noman said there was currently "no dialogue or even discussion" with the government and that so long as street protests continued, any future talks would be only about bringing down the government. On Saturday, protesters blocked Prime Minister Ali Mohammed Megaar from arriving at Sanaa University to hold talks with protesters there.
Protesters say they are frustrated with corruption and soaring unemployment in Yemen where 40 percent of its 23 million people live on $2 a day or less and a third face chronic hunger. Elsewhere in Yemen, suspected al Qaeda assassin teams shot dead two high ranking intelligence officials in separate marketplace attacks in two provinces, officials there said.
One intelligence officer, Abdel-Hamid al-Sherbani, was killed in the southern town of Zinjibar. He was one of around 50 security officers thought to be on an al Qaeda hit list. The second officer was killed in the eastern province of Hadramout. In Maarib, east of the capital Sanaa, suspected al Qaeda militants killed four police officers in a shooting ambush, a local official said. The police vehicle had been delivering supplies to forces when it was attacked.
(Additional reporting by Mohammed Ghobari in Sanaa and Mohammed Mukhashaf in Aden; Writing by Cynthia Johnston; editing by Philippa Fletcher)