Mexico asked President Bush Monday to veto the proposed 700-mile border fence, saying it would endanger lives while doing little to halt illegal immigration. "The Mexican government strongly opposes the building of walls in the border area between Mexico and the United States," said Ruben Aguilar, spokesman for President Vicente Fox. He said Mexico's Foreign Ministry planned to send a diplomatic letter to Bush urging him to veto the bill, which passed overwhelmingly in the U.S. Senate on Friday.The Senate also approved the first $1.2 billion down payment on the fence, which some experts say could cost as much as $9 billion. The plan entails running a barrier along mostly rural sections of the California and Texas borders and along nearly the entire length of Arizona.