WASHINGTON, June 15: The US Senate on Tuesday backed the Bush administration's plan to study a new generation of low-yield and earth-penetrating nuclear weapons, rejecting concerns that the research could spur an arms race.

Voting 55-42, the Senate defeated an amendment pushed by Democrats to slash 36.6 million dollars to study so-called bunker-busting nuclear weapons that would be used to destroy underground facilities as well as smaller nuclear arms.

The administration has said it has no plans to build such weapons, but wants to keep the door open to their development to deal with emerging threats. It successfully pushed Congress last year to repeal a 10-year-old ban on researching low-yield weapons of less than five kilotons.

Democrats said considering the new weapons takes nuclear warfare out of the realm of the unthinkable and encourages others to develop such weapons. -Reuters