U.S. counterterrorism officials believe Pakistani Taliban leader Hakimullah Mehsud is dead following a missile attack last month, a senior intelligence official said Wednesday in the strongest signal that Washington has offered about the militant's fate. Neither Pakistan nor the U.S. has officially confirmed the death of Mehsud, who commands an Al Qaeda-allied movement that is blamed for scores of suicide bombings and is suspected in a deadly attack on a CIA base in Afghanistan late last year. Mehsud's death would be the latest successful strike against suspected terrorists by the U.S. and its allies. The U.S. has recently stepped up attacks from unmanned aircraft in Pakistan, and a closer collaboration with Yemen has led to recent airstrikes there. President Barack Obama highlighted the increasing success of such attacks in his State of the Union address last week. The U.S. intelligence official, speaking on condition of anonymity to discuss sensitive security matters, said the conclusion that Mehsud is dead represents the best collective information of U.S. intelligence agencies. Since the attack, authorities have said they were growing increasingly confident Mehsud was dead. The official would not say what evidence the U.S. had gathered. The statement came after days of posturing by Pakistani Taliban officials, who first said they would prove their leader was alive and well, then reversed course and said they saw no need to prove it.