Yemen said yesterday it would not allow foreign fighters to infiltrate the country as the international jihadi network was swinging into action to counter Western efforts to bolster the feeble government, which is struggling to confront the Islamist threat.
"We tell our Muslim brothers in Yemen that we will cross the water between us and reach your place to assist you fight the enemy of Allah," declared Sheik Mukhtar Robow Abu Mansour, a senior official of the al-Shebab militia, as he addressed hundreds of newly trained recruits cheering "Allahu Akbar".
"Today you see what is happening in Yemen; the enemy of Allah is destroying your Muslim brothers. I call upon the young men in Arab lands to join the fight there."
On the one hand, it has to shore up a failing and often reluctant ally in the war against the Islamists, who launched the failed Christmas Day Detroit airliner attack from a base in Yemen.
On the other, it may energise hundreds of recruits among the fiercely anti-American tribes of Yemen, whose civilians have often been the casualties of airstrikes carried out by Yemeni warplanes acting on US intelligence. "The American entry into the war is very dangerous," said Abdulelah Haidar Shaea, a Yemeni expert on al-Qa'ida, who has met the Yemeni branch's leadership.
"If most people hate the government, then all the people hate America for its alliance with Israel and its wars in Iraq and Afghanistan."
He said witnesses to an attack before Christmas on an alleged al-Qa'ida base in the south had told him that US missiles had killed at least five civilians. The government claimed its warplanes had wiped out the al-Qa'ida leadership as well as Anwar al-Awlaki, a US-born Yemeni preacher who inspired both Umar Farouk Abdulmutallab, the Detroit bomber, and Major Nidal Hassan Malik, who shot dead 13 fellow US soldiers at the Fort Hood army base in Texas.
After the attack, Mr Shaea said that relatives of the victims took their bloodstained clothes to al-Qa'ida leaders and pledged allegiance. The government has been unable to confirm any of the deaths it claimed because its forces are unable to enter the area without being attacked by the well-armed tribes and al-Qa'ida.
Gregory Johnsen, of Princeton University, an expert on Yemen, said there was evidence that while the US military was being forced to invest in a weak and unpopular government, al-Qa'ida was building a powerful support base among the tribes.
Foreign al-Qa'ida members are even marrying into local tribes, while many of the fighters are native Yemenis who enjoyed the full protection of their clans.
"This development is both new and worrying because it has the potential to turn any counter-terrorism operation into a much broader war involving Yemen's tribes," Mr Johnsen said in a recent article, noting Said Ali al-Shihri, the deputy commander of al-Qa'ida, had moved his family from their native Saudi Arabia to Yemen.
"Yemen will not accept on its territory any presence by (foreign) terrorist elements and will be on guard against anyone who tries to act against its security and stability," Yemen's official Saba news agency quoted Foreign Minister Abu Bakr al-Kurbi as saying.
Saba said Mr Kurbi was "astounded" by the Shebab pledge to send militants to fight Yemeni government forces who have been battling al-Qa'ida.