As members of Congress unveiled new bills to ban assault weapons, city leaders on Thursday reaffirmed their support for stricter national gun-control laws.

“Too many times in the last few years, mayors have expressed shock at mass shootings,” said Philadelphia Mayor Michael Nutter. “Even more frequently, many of us must cope with gun violence that occurs on the streets of our cities day after day after day after day.”

Nutter, current president of the U.S. Conference of Mayors, outlined the organizations gun-control agenda in an open letter to Congress. At the top of the group’s list was “enact legislation to ban assault weapons and high-capacity magazines.” Nutter said 210 mayors had signed the letter as of Jan. 24.

In the letter, the group also calls on Congress to strengthen the national background check system and strengthen penalties for straw purchases of guns -- ideas also endorsed by the White House.

Sen. Dianne Feinstein, D-Calif., said her bill would ban 158 military-style firearms as well as high-capacity magazines with 10 rounds or more. The legislation would also exempt roughly 2,200 antique and hunting gun models. Finally, it would grandfather in existing firearms legally possessed at the date of enactment, pending a background check. Unlike the 1994 assault-weapons ban, Feinstein's proposal would not include a 10-year sunset provision. Rep. Carolyn McCarthy, D-N.Y., and Rep. Ed Perlmutter, D-Colo., are introducing a companion bill in the House.

When the ban's backers announced their bill's specifics, they came with props: a handful of rapid-fire rifles, including the exact model used in the Sandy Hook Elementary shooting in Newtown, Conn. Despite the attention paid to high-powered rifles, most gun homicides in the United States involve handguns. According to 2011 data collected by the FBI in its Unified Crime Reports, about 72 percent of the nation's gun murders involved a handgun, whereas less than 8 percent involved a rifle or shotgun.

Governors in Delaware, Colorado, Maryland and New York have embraced gun control as a top issue in this legislative session, as has President Barack Obama. However, any federal legislation would need to pass through a Republican-controlled House -- historically tepid on gun control -- and 24 Democrats in the House and Senate that received an A or A+ rating from the country’s largest gun lobby, the National Rifle Association.

“This is a really uphill battle,” Feinstein said.