WASHINGTON • The Republican- controlled United States Senate has rejected four competing gun-control measures just days after the Orlando club massacre, highlighting the partisan feuding over an issue set to resonate during a heated election year.

Republicans and Democrats voted down four amendments - two from each party - that would have limited some gun purchases, including those by suspected terrorists, even as both sides sought to appear keen to take action following the deadliest mass shooting in US history that left 49 dead at a gay nightclub in Orlando.

The two Democratic texts sought to bar those on Federal Bureau of Investigation (FBI) watchlists or no-fly lists from buying firearms, and to strengthen criminal and mental- health background checks for those seeking to purchase firearms at gun shows and on the Internet.

Republicans are opposed to those measures - in general, they oppose any effort to limit gun rights, saying that they are protected by the US Constitution's Second Amendment.

They proposed a 72-hour waiting period for those on FBI watchlists seeking to buy weapons, so that the government has time to seek a court order to block the sale if need be.

The second Republican proposal aimed to improve the background check system.

The Democrats rejected both Republican measures.

Such efforts often struggle to pass the Senate, where 60 out of 100 votes are needed for legislation to advance.

The Senate voted on similar measures in the wake of the December 2012 Connecticut school massacre and the San Bernardino attacks last year, but to no avail.

"Every single senator wants to deny terrorists access to guns they use to harm innocent civilians, but there's a right way to do things and a wrong way," said Republican Senator John Cornyn of Texas.

The second-ranking Democrat in the Senate, Mr Dick Durbin, was livid at the failure of lawmakers to come together on such a pressing issue after yet another shooting.

"The Senate turned its back on victims of gun violence from Orlando to San Bernardino, from Newtown to the streets of Chicago," he said.

Democrats know that they have only a slim chance of succeeding with gun reform ahead of the November elections. Their goal for now is to push the debate on guns - and turn it into a true campaign issue.

"Ultimately, the only way that you win this issue is by building a political infrastructure around the country that rivals that of the gun lobby," said Democratic Senator Chris Murphy.

Meanwhile, FBI transcripts showed that Orlando nightclub gunman Omar Mateen called himself an "Islamic soldier" and threatened to strap hostages into explosive vests in calls with police during the three-hour siege.

He told police negotiators to tell the US to stop bombing Syria and Iraq.

In the first call Omar made to a 911 emergency operator, he also pledged allegiance to Abu Bakr al-Baghdadi, leader of the Islamic State in Iraq and Syria (ISIS).

On Monday, the FBI and the State Department released partial transcripts of four calls between Omar and 911, as well as crisis negotiators, omitting his references to the ISIS leader, saying they did not want to provide a platform for propaganda.

But they later reversed their decision and released the unredacted version after criticisms from House Speaker Paul Ryan, Florida Governor Rick Scott and other political leaders.

AGENCE FRANCE-PRESSE, REUTERS