Yemeni special forces have been hunting down militant tribesmen in desert and mountain areas east and north of the capital Sana'a, where agents of Osama bin Laden's al-Qaeda terrorist network are thought to be living.
Yesterday 12 people were killed when security forces stormed a base of tribesmen suspected of kidnapping foreigners and blowing up a US-built oil pipeline, government officials said.
The search for terrorist suspects has intensified, according to a government official, since President Ali Abdullah Saleh's visit to Washington last month. There was speculation before the visit that Washington would strike Yemen in the second phase of the anti-terror campaign. Somalia, Iraq and Sudan were also cited as possible future targets of the US-led war on terrorism once the Afghan campaign is over.
According to US analysts, Mr Saleh was under intense pressure to co-operate more fully with FBI investigations into the suicide attack on the USS Cole in Aden harbour in October last year, in which 19 sailors died.
In meetings with President Bush, Mr Saleh is believed to have promised to respond to US concerns "provided he was given some time and space" to take account of domestic politics, said a senior Yemeni official.
But Yemen's domestic realities inhibit both co-operation and disclosure about many hardliners who may fall under the US definition of "terrorist sympathisers". The term, analysts point out, could apply to tens of thousands of ordinary Yemenis who have a deep-seated loathing of the US relationship with Israel.
According to Mr John Duke Anthony, president of the National Council on US-Arab Relations and a consultant to the Defence and State departments, there is also fierce resentment after what was seen as heavy-handed behaviour by US agents after the Cole incident.
Tucked away in the desert and mountain vastness at the southern end of the Arabian peninsular, Yemen's 19 million people are among the world's poorest, with an average annual per capita income of less than $500.
The country's proximity to Saudi Arabia, and its 300-mile coastal plain close to the main shipping lanes through the Bab al Mandab strait at the southern end of the Red Sea, give an extra dimension to the importance of the country's stability.
Operating what one author called a "despotic democracy", Mr Saleh would seem to have overwhelming support and sweeping powers. But rigged elections have alienated Yemen's Islamist opposition which can count on support from up to half the population, some believe, even though it has only one sixth of the parliamentary seats.
Kalashnikov rifles outnumber the population by three to one and shoot-outs are a common way of settling scores. Foreigners are regularly kidnapped, to be used as bargaining chips to force parliament to deliver on promises of roads, wells or clinics.
Estimates on the number of people who might be seen as militants vary "depending on one's definition of a militant and the circumstances prevailing on the day," says a former British ambassador in the Middle East. "Most of it boils down to cash. If people cannot earn money or are otherwise alienated, they become extremists."
Saudi-born Osama bin Laden, whose family originates from Yemen's Hadhramaut valley, is one such example.
The large majority of militants who, like bin Laden, returned home after fighting against the Soviet Union in Afghanistan in the 1980s made their peace with Mr Saleh, and the president gave them another opportunity to fight during Yemen's civil war in 1994.
Since 1994, the US has become progressively more involved in Yemen's internal affairs, and terrorist attacks against the US and British interests have continued. The most serious took place in December 1998, following US and British bombing of Iraq.
Despite the US need to work with Mr Saleh on rooting out extremist cells in Yemen, analysts fear that US pressure will only heighten tensions.
"The great lesson of the 120-year British presence in Yemen was that . . . the military presence was the cause of extremism."