A power vacuum may be developing in Yemen as the country's embattled president remains in Saudi Arabia. Ali Abdullah Saleh went there for medical treatment after he was injured in a bomb attack on his presidential compound. Meanwhile his forces remain in a stand-off with tribesmen determined to topple the Saleh regime and the government is also battling Islamic militants. On Thursday, Yemeni officials said government troops killed several suspected al-Qaeda militants in the country's south. And in the middle of all that the New York Times reports that American drones and fighter jets have intensified a U-S campaign of air-strikes against militants. The paper's national security correspondent Mark Mazzetti wrote the story.