A makeshift memorial in Brussels left after Tuesday’s bomb attacks. (Nicolas Maeterlinck/Belga/ AFP)

Congressional leaders on Tuesday said the bombings in Brussels underscore the need to accelerate the military campaign against terrorist groups and to boost airport security in the United States.

Blasts that struck a major international airport and a metro station frequented by European diplomats put Brussels on lockdown Tuesday amid fears the attacks were carried out in retaliation for the recent capture of Salah Abdeslam, the presumed mastermind of the November Paris attacks.

The Islamic State, also known as ISIL or ISIS, took credit for the attacks.

[The Islamic State claims responsibility for the Brussels attacks]

“Our nation stands in solidarity with the people of Belgium and we will renew our determination to prevent more senseless violence against the innocent,” Senate Majority Leader Mitch McConnell (R-Ky.) said in a statement. “Defeating ISIL, al Qaeda and its affiliates will require concerted action by the military, our intelligence community, and our international partners.”

After three blasts left more than 30 people dead in the Belgian capital, U.S. House Speaker Paul Ryan urged international cooperation in response to the attacks saying, "We must confront this threat together." (Reuters)

House Speaker Paul D. Ryan (R-Wis.) also called for international cooperation against terrorist groups and sought to play down worries that Washington could soon be attacked.

“We have reached out to the intelligence community and I have received some updates this morning and I have absolutely no reason to believe that there’s a threat here,” he told reporters.

Some top lawmakers said the bombings should lead to a push to tighten security at airports.

Sen. Charles E. Schumer (D-N.Y.) said Congress should use the pending reauthorization of the Federal Aviation Administration to create tighter screening requirements for Transportation Security Administration officers and aviation workers and to boost funding for tightening airport perimeter security.

“You can never be too careful,” Schumer told reporters. “We have to look at what happened in Brussels and in Europe and, you know, tighten up even more.”

House Majority Leader Kevin McCarthy (R-Calif.) pointed out that a bill the House plans to vote on soon would require comprehensive security assessments of overseas airport security and better cooperation between the Department of Homeland Security and its foreign counterparts. On Monday night, the House passed a bill requiring the department to produce an annual scorecard of foreign countries’ border security efforts.

After last year’s terrorist attacks in Paris and San Bernardino, Calif., Congress stiffened the requirements for participating in a popular visa waiver program that expedites tourism and short-term business travel to the United States. The House also passed legislation that would halt the resettlement of refugees from Syria and Iraq, the two countries with the largest Islamic State presence, in the United States, but that bill was blocked by Democrats in the Senate.

Republican front-runner Donald Trump calls Brussels "a disaster," the morning after deadly blasts rocked the Belgian capital. Democratic front-runner Hillary Clinton urges the U.S. to "reaffirm our solidarity with your European friends." (Sarah Parnass/The Washington Post)

Rep. Richard Hudson (R-N.C.), who wrote an early draft of the refugee resettlement legislation, said he hopes the attacks will spur the Senate to reconsider the bill.

“Brussels underscores the need to be vigilant,” he said.

On the campaign trail, Republican presidential front-runner Donald Trump caused a controversy in December when he called for a temporary ban on all Muslims entering the United States following the Paris and San Bernardino attacks. The proposal drew rebukes from congressional leaders in both parties.

On Tuesday, he again called for restricting entry to the United States without specifically reiterating his call for a temporary ban on Muslims.

“I would close up our borders to people until we figure out what is going on,” he said in an interview with Fox News. He added: “We’re taking in people without real documentation. We don’t know where they’re coming from. We don’t know what they’re — you know, we don’t know where they’re from, who they are. You look at them and look at them from any standpoint — they could be ISIS, they could be ISIS-related.”

Republican leaders did not comment on Trump’s demands. But some Democrats refuted the idea that barring the doors to the country would help.

“I don’t think the answer is to keep people out of the United States,” said Sen. Jeanne Shaheen (D-N.H.), who was in Brussels for a security conference last week and left the city Monday. She added that the United States needed to embrace “more understanding and tolerance” to determine “how we can cooperate with people who may not be exactly like us to address [this threat] together.”

Shaheen described the “heightened presence” of police and military guards on the streets of Brussels and in the airport that was attacked as noticeable in recent days. She was in the city when Abdeslam was captured, a moment she said seemed to bring “some closure” for locals and authorities in Brussels — a city that has become accustomed to living on heightened alert.

But that closure was soon punctured by the attack, which Shaheen called “a despicable act by cowards” deliberately targeting “places where people will be. They’re targeting symbols of civilization … just as we saw with the 9/11 attacks in the United States and with the Paris attacks.”

For the most part, lawmakers’ reactions to the Brussels bombings steered clear of political finger-pointing. But the chairmen of the House and Senate armed-services committees used the occasion to restate their grievances with the Obama administration for not giving Congress a written “strategy” to fight the Islamic State — and not doing enough to rout the extremist network militarily.

“Time has never been on our side in this conflict, and the failure to recognize the urgent realities of the war against ISIL will carry a grave price for our nation and our people,” Sen. John McCain (R-Ariz.) said, calling the Brussels attack “sadly predictable.”

[Brussels attack intensifies pressure on Obama to explain Islamic State strategy]

House Armed Services Committee Chairman Mac Thornberry (R-Tex.) said the attacks highlight the need to beef up U.S. military budgets.

“The world is growing more dangerous; we have cut our military too much; and it is up to the political leadership in this country to take the action necessary to enable our service men and women to defend American lives and interests,” he said.

Kelsey Snell and Paul Kane contributed to this report.