A Republican-backed proposal to tighten screening procedures on refugees fleeing war from Syria and Iraq was blocked by Democrats in the Senate on Wednesday.

The bill -- which passed in the GOP-controlled House last November -- aimed to slow down the entry process of Syrian and Iraqi refugees into the United States by requiring high-level U.S. officials to clear each applicant to ensure that they posed no security risk. The White House, however, denounced the measure as untenable and President Barack Obama had promised to issue a veto if it passed both branches of Congress, reports The Wall Street Journal.

Senate Democrats narrowly blocked the legislation in a 55-43 vote. As a result, Republican Senate Majority Leader Mitch McConnell, R-Ky., failed to gain enough votes to reach the 60-vote threshold needed to proceed without congressional hurdles.

According to Republicans, the tighter screening measure is needed to prevent terror attacks on American soil carried out by the Islamic State militants and other extremist groups.

"This bipartisan bill would allow Washington to step back, take a breath and ensure it has the correct policies and security screenings in place," said McConnell before the vote, reports Reuters.

House Speaker Paul Ryan, R-Wisc., also condemned Democrats for blocking the legislation.

"Senate Democrats are making it that much harder for us to keep Americans safe," said the House Republican leader, according to The New York Times. "Their vote is irresponsible in a time of grave threats. Even the administration's top law enforcement officials say there are gaps in our refugee program that terrorists can exploit."

However, Democrats argued that the bill was an attack on people fleeing war torn countries. They also accused Republicans of holding the vote to give GOP senators running in the 2016 presidential election an opportunity to support legislation touted as tough on security. All three candidates, Texas Sen. Ted Cruz, Kentucky Sen. Rand Paul and Florida Sen. Marco Rubio, left the campaign trail to vote for the bill.

"Over and over again, Republicans remain committed to pledging loyalty to the divisive platform they have built for Donald Trump," said Nevada Democratic Sen. Harry Reid, tying the refugee screening bill to Donald Trump's call to ban Muslims from entering the U.S.