President Barack Obama has sought to rally US public support for proposed background checks for all gun buyers.
Mr Obama touted new gun control measures enacted in Colorado - the scene of two of the deadliest gun massacres in American history - as "a model of what's possible".
He is aiming to revive stalled momentum in Congress for several gun control measures, including universal background checks for gun buyers that he called for after a gunman killed 20 children and six adults at a Connecticut school in December.
The US Senate is set to take up gun control next week.
Speaking in a Western state that Mr Obama noted has a strong tradition of gun ownership and hunting, the president said that taking action to reduce gun violence does not have to infringe on Americans' gun rights, enshrined in the US Constitution's Second Amendment.
"There doesn't have to be a conflict between protecting our citizens and protecting our Second Amendment rights," Mr Obama told a cheering crowd in Denver.
Democratic Governor John Hickenlooper last month signed into law legislation passed by Colorado legislators to require universal background checks for gun buyers and ban ammunition magazines with more than 15 rounds.
"I've come to Denver today in particular because Colorado is proving a model of what's possible," Mr Obama said, adding that the state has shown that "practical progress" can be made.
Mr Obama met privately with law enforcement and elected officials as well as relatives of victims of two Colorado mass shootings: at a movie theatre last year in the Denver suburb of Aurora and at Columbine High School in 1999.
Mr Obama devoted most of his speech at the Denver Police Academy to trying to build the case for expanding the existing background checks to cover all gun buyers.
Loopholes in the law have exempted many gun buyers from such checks.
"Now understand, nobody is talking about creating an entirely new system. We are simply talking about plugging holes, sealing a porous system that isn't working as well as it should," Mr Obama said.
"If you want to buy a gun, whether it's from a licensed dealer or a private seller, you should at least have to pass a background check to show you're not a criminal or someone legally prohibited from buying one. And that's just common sense," Mr Obama added.
No major gun legislation has passed the US Congress since 1994, but Mr Obama has made gun control one of his top legislative priorities.
Opinion polls show strong support for background checks and other gun control proposals, but gun rights advocates led by the National Rifle Association have lobbied fiercely against any new measures.
Theatres of war
In Denver, Mr Obama mentioned some of his other gun control proposals - reinstating the ban on assault weapons and cracking down on high-capacity ammunition clips - that already appear to have little chance of passing the Democratic-led Senate, let alone the Republican-controlled House of Representatives.
"I don't believe that weapons designed for theatres of war have a place in movie theatres. Most Americans agree with that," Obama said.
Meanwhile, Connecticut lawmakers have voted to approve a new gun-control bill, which supporters described as one of the toughest in the United States, in response to the Sandy Hook Elementary School shooting.
The new law would require background checks for private gun sales, ban the sale of high-capacity ammunition clips of the kind used at Sandy Hook, and require current owners of those large clips to register them with the state.