Mark Mazzetti is reporting that The Obama administration has intensified the American covert war in Yemen, exploiting a growing power vacuum in the country to strike at militant suspects with armed drones and fighter jets, according to American officials.

The acceleration of the American campaign in recent weeks comes amid a violent conflict in Yemen that has left the government in Sana, a United States ally, struggling to cling to power.  Yemeni troops that had been battling militants linked to Al Qaeda in the south have been pulled back to the capital, and American officials see the strikes as one of the few options to keep the militants from consolidating power.

On Friday, American jets killed Abu Ali al-Harithi, a midlevel Qaeda operative, and several other militant suspects in a strike in southern Yemen.  According to witnesses, four civilians were also killed in the airstrike.  Weeks earlier, drone aircraft fired missiles aimed at Anwar al-Awlaki, the radical American-born cleric who the United States government has tried to kill for more than a year. Mr. Awlaki survived.

The recent operations come after a nearly year-long pause in American airstrikes, which were halted amid concerns that poor intelligence had led to bungled missions and civilian deaths that were undercutting the goals of the secret campaign.

Officials in Washington said that the American and Saudi spy services had been receiving more information -- from electronic eavesdropping and informants -- about the possible locations of militants.  But, they added, the outbreak of the wider conflict in Yemen created a new risk: that one faction might feed information to the Americans that could trigger air strikes against a rival group.

A senior Pentagon official, speaking only on condition of anonymity, said on Wednesday that using force against militants in Yemen was further complicated by the fact that al-Qaeda operatives have mingled with other rebels and antigovernment militants, making it harder for the United States to attack without the appearance of picking sides.

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