Suspicion fell instantly on Al Qaeda’s affiliate in Yemen, which has been fighting a bloody battle in recent days against the Yemeni military for control of towns in Yemen’s lawless south. The United States, increasingly concerned about the militants’ widening influence in Yemen, has assisted the fight with a stepped-up campaign of drone strikes and military assistance.
The suicide bombing brought scenes of horrific carnage to a central square in Yemen’s capital, which had been spared the worst of the insurgent violence.
“I saw arms and legs scattered on the ground,” said one young soldier named Jamal. “The wounded people were piled on top of each other, covered with blood. It was awful.”
A video of the parade ground posted on YouTube showed throngs of rehearsal participants running in panic and a pile of motionless uniformed bodies following the explosion.
The bombing came amid an intensive battle by the Yemeni military to retake a southern town that has been controlled by militants allied with Al Qaeda’s affiliate in Yemen
The parade rehearsal bombing came as the Defense Department in Washington confirmed that three American civilian contractors helping to train Yemen’s coast guard were attacked on Sunday by militant gunmen in Yemen’s port city of Hodeida. A Pentagon spokesman, Cmdr. Bill Speaks, was quoted by The Associated Press as saying the injuries were minor. Yemeni officials had said earlier that the instructors were members of the United States Coast Guard, which the Coast Guard had denied.
The suicide bombing attack in Sana appeared to catch the Yemen defense forces totally by surprise and presented a major new challenge to President Abdu Rabbu Mansour Hadi. He took power in February from former President Ali Abdullah Saleh, the longtime autocratic ruler whose unwillingness to cede power had long been an underlying cause of the mayhem in the country.
Last week, Yemen’s Defense Ministry issued a warning about a suicide bomber roaming the capital, and it was not clear whether Monday’s bomber was the same person.
Witnesses said the attacker walked from the western part of Saba’een Square, dressed in military clothes, and detonated a suicide belt just before the defense minister, Nasser Ahmed, and his immediate subordinates had been expected to greet the troops. Most of the casualties were members of the Central Security Organization, a paramilitary force commanded by Yahya Saleh, a nephew of the former president, according to several survivors.
As depicted, the parade ground attack bore a resemblance to attacks on NATO forces in Afghanistan, where insurgents or disgruntled soldiers have also used army uniforms as camouflage to infiltrate the ranks of their unsuspecting targets.
The violence came at a particularly delicate time with Yemen drawing increased concern in the United States that it is unable to curb the influence of Islamic militants after the months of political instability.
Last week, the Yemeni government said that it had intensified efforts to take back southern towns from Islamist insurgents with airstrikes and ground assaults that left dozens of people dead, including some civilians, according to officials and witnesses on the ground.

Robert F. Worth reported from Washington and Alan Cowell from London. Rick Gladstone contributed reporting from New York. copy :http://www.nytimes.com/