IE 11 is not supported. For an optimal experience visit our site on another browser.

John Kerry: We're Determined to Thwart Foreign Fighters

Kerry also brushed off criticism that Obama should have rushed back to the U.S. from Cuba after the Brussels bombings occurred.

With evidence pointing to an ISIS-linked terror cell as the group behind the carnage in Brussels, Secretary of State John Kerry said the U.S. has stepped up its efforts to thwart foreign fighters looking to cause havoc outside of Syria and Iraq.

"This is one of the parts of the war that we are fighting. We have an entire focus on foreign fighters," Kerry told NBC News on Friday. "In fact a month ago, here in Belgium, we had a foreign fighter search team here working with the Belgians in order to try and make sure that they were dealing appropriately with this potential at any time in the future."

Related: Suspect Hailed as 'Major Arrest' Tied to Paris Ringleader

But stopping Tuesday's attacks in the Belgian capital would have proved difficult, Kerry said, because the team of terrorists suspected of carrying out the deadly attacks had been in the country for some time.

Intelligence sources have told NBC News that one of the suicide bombers at the Brussels airport, Najim Laachraoui, also had a hand in making the suicide vests used by the terrorists who attacked Paris last November.

The brothers who took part in the Brussels siege and were killed, Ibrahim and Khalid El Bakraoui, also set up a safe house and secured weapons for those who took part in Paris, sources said.

Kerry said President Barack Obama is focused on "upping what we are doing in Syria" in order to strike ISIS at home — and prevent the terror group from sending more of its trained foreign recruits back to their native countries to carry out attacks.

Related: Police Raids in Paris Foil Planned Terrorist Attack: Officials

Kerry also brushed off criticism that Obama, who is currently on a tour of Latin America, should have rushed back to the U.S. after the Brussels bombings occurred. Two Americans are among the victims killed — at least 31 people between attacks on the city's airport and a subway station, a senior official told NBC News.

Kerry said that as the attacks unfolded, the president in Cuba was in direct talks with the prime minister of Belgium.

"Nobody knew at that point in time what the situation was and the president was in immediate contact with people," Kerry said, "and at that point there was no rationale to cut the trip short — none whatsoever."