Yemen's security forces have clashed with suspected members of al-Qaeda as they hunted fighters behind a deadly attack on a government intelligence compound in the southern city of Aden.
A security official told the Reuters news agency that fighting had broken out during a search of houses in the port city's Saada district following the attack last Saturday that left 11 people dead.
Gunmen wearing military fatigues attacked the police intelligence building on Saturday, killing seven security officers, three women and a seven-year old boy, and freeing several detainees being held there.
Friday's fighting ended in several arrests, the security official said, but declined to give further details.
Yemen's interior ministry has called for a security alert in Aden to prevent arms or fighters entering the city, which is the impoverished country's economic hub.
In a statement on its website, the ministry asked for "security bodies to tighten their grip on Aden's coast and to keep it under constant watch to prevent the infilitration of any terrorist elements into the city or the smuggling of weapons".
Yemen has attracted the attention of the international communuity since an al-Qaeda inspired group claimed responsibility for a thwarted attempt to blow up an airliner over the US city of Detriot in December last year.
Analysts say Saturday's attack show a shift in al-Qaeda tactics in Yemen with its fighters turning their attention from Western targets to the country's security forces.
"Al-Qaeda now feels under great pressure in Yemen, not only from the Yemenis but also from the United States," Mustafa Alani of the Gulf Research Centre said. "Its members are suffering from a sense of uncertainty and they have become very isolated... This attack was a show of strength."
Until the December bomb-attempt, many had criticised Sanaa's counter-terrorism efforts as half-hearted. But following the attack, the US has more than doubled its military aid to Yemen and provided "technical support" to the cash-strapped government of Ali Abdullah Saleh, the president.
This has seen an escalation in counter-terrorism efforts from the Yemeni government, analysts say.
"They tried to deprive al-Qaeda from the safe haven they enjoyed. We are witnessing a major shift here," Alani said.
The day before Saturday's attack, al-Qaeda's regional branch in Yemen called on local tribesmen to take up arms against the government.
"God willing, we will set the ground on fire beneath the tyrant infidels of Ali Saleh's regime and his American collaborators," the group said in a statement.
Yemen is struggling to curb a separatist movement in the south of the country while maintaining an uneasy ceasefire with Shia Houthi rebels in the north. Experts have said that Saturday's attack is an attempt to exploit uncertainty in the country.