WASHINGTON (AFP) - The US Senate will hold votes on Wednesday on legislation aimed at curbing gun violence, even though senior Democrats are unsure if there is sufficient backing for background checks on firearms sales.

Majority Leader Harry Reid said he scheduled up to nine votes on amendments, including one that expands background checks to all commercial sales, and others that ban assault weapons, restrict the size of ammunition clips and criminalise gun trafficking.

Republican substitute amendments that largely boost gun rights, including one that addresses the concealed-carry rights of gun owners, are also among those to be voted on.

Mr Reid struck a deal with top Republican Mitch McConnell to hold the votes beginning at 4:00 pm (4am Thursday, Singapore time), on the most significant gun bill in nearly 20 years, but it remained unclear late on Tuesday whether he had the 60 votes needed to ensure approval of the background check measure, the bill's core amendment.