A day after refusing to regulate gun-show sales in a highly controversial vote, Senate Republicans moved Thursday to close a gun- law loophole and reduce teen access to semi-automatic assault weapons such as AK-47s and Uzis.

All but six Republicans voted Wednesday night against a proposal by New Jersey Democrat Frank Lautenberg that would require instant criminal background checks for all transactions at gun shows. Such checks are now required for all sales by legal dealers, but not from more informal show vendors.

The Senate instead backed voluntary checks at gun shows. That measure, sponsored by Idaho Republican Larry Craig, also weakened or repealed some existing gun laws, according to Democratic critics including Attorney General Janet Reno.