The last U.S. commando still missing in Afghanistan (search) is being held by the Taliban (search) and rebel leaders have decided to kill him, a purported spokesman for the group said Thursday.

The spokesman, Mullah Latif Hakimi (search), offered no proof to back up the claim, which he has made previously. U.S. military spokeswoman Lt. Cindy Moore responded by saying: "We hope he is not in harm's way. We are making every effort to locate him."

The commando is the last of a four-member U.S. Navy SEAL (search) team missing for 10 days in Kunar province (search), near the Pakistani border. One of the men was rescued and the other two have been found dead.

About 300 troops and several aircraft are searching for the U.S. Navy SEAL in the rugged mountains in eastern Afghanistan, Moore said.

Hakimi has said previously that the Taliban are holding the commando. But his information has in the past frequently proven exaggerated or untrue, and his exact tie to the Taliban leadership cannot be independently verified.

"This American will never be forgiven. Definitely he will be killed," Hakimi said. He said the group would release a video after the man's death.

Hakimi said he was last in contact on Wednesday with the rebels who he says are holding the American and was told the captive's health was good and that he had not been abused. He said the U.S. service member was being held in a house in Kunar.

The eastern province has long been a hotbed of militant activity and a haven for fighters loyal to renegade former premier Gulbuddin Hekmatyar (search), who is wanted by the United States. U.S. officials said Al Qaeda fighters also were in the region. Usama bin Laden (search) was not said to be there — though he is believed to be somewhere along the Afghanistan-Pakistan frontier.

The region's wooded mountains are popular with militants because they are easy to infiltrate from neighboring Pakistan and have plenty of places to hide.

On Saturday, a U.S. airstrike in the region killed as many as 17 civilians, prompting a strong rebuke from the Afghan government.

A special forces helicopter carrying reinforcements to the mountain area crashed on June 28, killing all 16 Americans on board, the deadliest single attack on the U.S. military since the war here began in 2001.

The claim by the Taliban follows an unprecedented spate of insurgent violence that has left about 700 people dead and threatened to sabotage three years of progress toward peace. Afghan officials insist the violence will not disrupt landmark legislative elections slated for September.

Elsewhere in Afghanistan, suspected Taliban rebels late Wednesday attacked a government office, about 40 miles south of the Afghan capital, Kabul, local police chief Khan Mohammed said.

Police guarding the building fought back during a two-hour gunbattle before the insurgents fled. No officers were killed, he said. The fighting was the closest by suspected Taliban rebels to Kabul in months.