听力原文： The U.S. military says the helicopter was on an anti-guerilla mission and was transporting forces when it went down on Tuesday near Asadabad, the capital of the mountainous Kunar province bordering Pakistan. U. S military spokesman Colonel Jim Yonts told reporters in Kabul that the fate of 17 U.S. servicemen on board is unclear. He says the helicopter came under fire from the ground as it was approaching its landing zone but it is not clear whether this caused the crash. 'Initial reports indicate the crash may have been caused by hostile fire. The status of the service members remains unknown. Coalition and Afghan national forces moved into positions around the crash site and blocked enemy movement toward or away from the site. ' Colonel Yonts says a major operation is underway in the region to eliminate bases of terrorist organizations, but gave no other details. Provincial authorities say a rocket hit the helicopter and a spokesman for the now-ousted Taleban regime is reported as claiming its fighters shot down the aircraft. Roughly three months ago, another U. S military helicopter came down in a dust storm in Ghazni province, killing 18 soldiers on board. At least 14 other U.S troops have been killed in increased militant activity led by Taleban guerillas since March. Afghan and U.S. officials say the violence is aimed at derailing Afghan parliamentary elections in September. The Afghan government has vowed the palls will be held on time despite the surge in violence. The United States, which is leading an anti-terrorism coalition force in Afghanistan, has promised to step up anti-militant operations to reduce the threat to the elections. On Tuesday, senior military and diplomatic representatives from Afghanistan, Pakistan and the United States met in Kabul to discuss steps to improve security and ensure the success of the elections in Afghanistan. The meeting of the tripartite commission took place amid growing U.S. and Afghan concerns that Taleban rebels are still using border areas of Pakistan to launch attacks. How many US soldiers were there on board?