The former secretary of state won a sweeping victory in this week's Democratic primary in New York.
Democratic frontrunner for US president Hillary Clinton strongly criticized the gun lobby on Thursday while meeting families of shooting victims days before the next round of primary elections.
"It just doesn't make sense to me. I find it absolutely indefensible, the arguments that are made by people who will not accept responsibility for what is going on in our country," she said at an event in Hartford, Connecticut.
"When you take a stand against gun violence and against the gun lobby you are subjected to some of the most vile harassment on the Internet that you can imagine. It is beyond decency," she added.
"There is an organized effort, again, to intimidate, to silence."
Clinton called for "comprehensive gun safety reform" to be at the top of the agenda along with better mental health treatment to stop young people ending up in prison because they have undiagnosed mental health conditions.
"We just have too many guns in this country in the wrong hands," she said. "We have to address it."
But she stopped short of proposing any specific reforms and declined to say how far she would go in seeking to implement gun control.
President Barack Obama, hobbled by America's powerful gun lobby, has argued for executive measures regulating the sale and purchase of weapons, controversially bypassing Congress.
Clinton called Obama's set of executive actions "a very good beginning" and promised, if elected president in the November general election, to "do everything I can to implement those and act on those."
Around 30,000 people are killed in America every year by guns.
The former secretary of state won a sweeping victory in this week's Democratic primary in New York and is looking to match that success when Connecticut, Delaware, Maryland, Pennsylvania and Rhode Island vote on April 26.
She has sought to portray herself as Obama's heir and has repeatedly criticized her opponent, Vermont senator Bernie Sanders, for being weak on gun control.
Clinton currently leads among Democrat voters in Connecticut on 50 to 42.5 per cent for Sanders, a tighter margin than her win in New York, according to a RealClearPolitics poll average.
On the national level, she is just 1.4 percentage points ahead of Sanders on 47.7 to 46.3 per cent, based on the RealClearPolitics average.