A vital NATO supply route to Afghanistan that currently goes from Pakistani seaports through restive tribal areas and negotiates the mountainous border between the countries is seen as an Achilles' heel in U.S. war efforts. In response, officials are studying much longer overland routes from Europe, The Washington Post reported Wednesday.

U.S. Defense Department documents obtained by the newspaper indicate military planners are considering supply routes through Europe, the Caucasus and Central Asia.

The U.S. Transportation Command sent a notice to potential contractors in September saying, "strikes, border delays, accidents and pilferage" in Pakistan and the risk of "attacks and armed hijackings" in Afghanistan posed "a significant risk" to supplies for Western forces in Afghanistan, the Post reported.

"From Karachi to Kabul there is trouble. The whole route is insecure," a truck driver from the Pakistani tribal town of Landikotal told the newspaper.