HAVANA – President Barack Obama pledged to “do whatever is necessary” to help Belgian authorities seek justice for the more than two dozen people who were killed Tuesday in explosions at the Brussels airport and the subway system.

“We stand in solidarity with them in condemning these outrageous attacks against innocent people,” Obama said in Havana, where he was closing a historic three-day visit. He commented on the events in Brussels at the top of a keynote address to the Cuban people.

“We will do whatever is necessary to support our friend and ally Belgium in bringing to justice those who are responsible,” Obama said. He said America’s thoughts and prayers are with the people of Belgium.

Obama said Tuesday’s attacks provided yet another reminder “that the world must unite,” regardless of nationality, race or faith in “fighting against the scourge of terrorism.”

“We can and we will defeat those who threaten the safety and security of people all around the world,” he said.

Obama was briefed earlier Tuesday on the attacks. He also telephone Prime Minister Charles Michel to offer condolences.

Secretary of State John Kerry, who spoke by telephone from Cuba with the Belgian foreign minister, said in a statement that the U.S. was working “to determine the status of all American citizens in Brussels.” The embassy there issued a statement telling Americans to stay where they are and “take the appropriate steps to bolster your personal security.”

The State Department said it was looking into reports that at least three Americans may have been wounded in the attacks, but cautioned that those reports were preliminary and unconfirmed.

At least one of the attacks was believed to be caused by a suicide bomber, and Belgium raised its terror alert to its highest level.

Rep. Adam Schiff, D-Calif., the ranking member of the House intelligence committee, said the attacks “bear all the hallmarks” of an Islamic State group coordinated or inspired attack. His staff said he received a preliminary briefing Tuesday from U.S. officials. Schiff says it’s unclear if encrypted communications played a role in the attacks but noted that the Brussels attacks occurred despite the city being under constant vigilance.

The U.S. Department of Homeland Security said it was closely monitoring the unfolding events and “would not hesitate to adjust our security posture, as appropriate, to protect the American people.”

DHS reiterated that members of the public should report any suspicious activity in their communities to law enforcement authorities.

Attorney General Loretta Lynch was also briefed on the attacks, Justice Department officials in Washington said. They said the Justice Department and the FBI was coordinating with other U.S. government agencies, as well as with Belgian counterparts.

Last week U.S. Homeland Security Secretary Jeh Johnson said Homeland Security officials constantly monitor world events and evaluate whether there is a need to either publicly raise the nation’s security posture or issue another bulletin via the government’s National Terror Advisory System.

Such a bulletin was issued in December advising the public that federal law enforcement was concerned about the possibility of homegrown violent extremists and terrorist-inspired individuals.

Sen. Susan Collins, R-Maine, a member of the Senate Intelligence Committee and a former chairman of the Homeland Security Committee, said in a statement, “The United States stands firmly with the government and the people of Belgium in the face of this horrific act of terrorism.

“Today’s terrorist attack is another stark reminder that ISIS poses a direct and very dangerous threat to the American people and to our allies in Europe so long as ISIS has safe havens to operate from in Syria, Iraq, and Libya. I want the families of the victims to know that the United States will redouble its efforts to work with our allies to disrupt and prevent these vicious attacks and to pursue and capture those responsible.

“As a member of the Senate Intelligence Committee, I will be receiving further information and analysis from the National Counter Terrorism Center throughout the day.”

Sen. Angus King, I-Maine, said his thoughts are prayers are with the people of Belgium.

“While authorities are still working to uncover more information, Senator King has been briefed on the attacks today by counterterrorism officials as part of the ongoing Congressional delegation trip, which began in Eastern Europe and is focused on national security,” Scott Ogden, spokesman for King. “He will continue to receive updates throughout the day as more information becomes available. Acts of terrorism like these are a direct affront to the freedom and liberty of people around the world, and the United States stands shoulder to shoulder with Belgium as it seeks to bring to justice those who are responsible for this atrocity.”

Rep. Bruce Poliquin, R-2nd District, said people must stay strong in the face of the attacks.

“These extremist groups pose a threat to the safety of our Nation and our allies around the world and we must take necessary steps to strengthen our national security, secure our borders and protect Americans at home and abroad,” he said in a news release.

In a statement, Rep. Chellie Pingree, D-1st District, said her thoughts are also with the people of Europe and the victims of the attack.

“The American people must stand with our friends and allies at times like this,” she said. “We will remain strong in fighting terrorism and at the same time not let these cowardly attacks blind us with fear or cause us to forget our core values.”

Caldwell and Associated Press writer Tami Abdollah contributed reporting from Washington. Also includes staff reports.

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