U.S. officials said that illegal tunnels running under the border with Mexico are becoming increasingly common and sophisticated.
James Dinkins of Immigration and Customs Enforcement (ICE) told the Senate that 154 illicit tunnels crossing the border have been discovered since 1990.
"Over the past several years, law enforcement has seen a marked increase in the number and sophistication of tunnels," said the official.
He said most of these passageways, used to traffic drugs and humans, were located on the southwest part of the border.
In November 2010 a border task force found a tunnel half a mile long equipped with rail, electricity and ventilation systems. The construction cost of the tunnel was estimated to exceed one million dollars. A shorter tunnel, also with ventilation and electricity, was found in May on the Arizona border.
At the hearing, Senator Dianne Feinstein announced plans enhance a 2007 law against the tunnels. She proposed that the bill provide law enforcers “additional tools to locate tunnels, identify criminals and punish those involved.”