The United States has ramped up intelligence cooperation and will review international efforts to combat Islamic State militants after the Brussels attacks during a nuclear summit with world leaders next week, President Barack Obama said.

In his weekly address broadcast on Saturday, Obama expressed condolences to the families of the Americans and others killed or hurt in the suicide bombings in Brussels on Tuesday.

"Yesterday, we learned that at least two Americans were killed. We pray for their families and loved ones," he said. "At least 14 Americans were injured. And we pray for their full recovery, along with everyone else affected by these attacks."

Obama returned on Friday from a trip to Latin America, where he took criticism for attending a baseball game in Cuba and for dancing the tango in Argentina in the aftermath of the attacks.

The president did not address that criticism in his address, but he emphasized that fighting Islamic State, also known as ISIL, was a top priority that had included greater US intelligence cooperation.

"We're also working to disrupt plots against the United States and against our friends and allies. A team of FBI agents is on the ground in Belgium supporting the investigation," he said.

"We've ramped up our intelligence cooperation so that we can root out ISIL's operations. And we constantly review our homeland security posture to remain vigilant against any efforts to target the United States."

Obama will meet with foreign leaders including Chinese President Xi Jinping for a nuclear summit in Washington on Thursday and Friday. He said he would use that opportunity to review joint counter-terrorism efforts and ensure the world remained united on the topic.

The president also pushed back again against rhetoric from Republican presidential candidates aimed at Muslims within the United States.

"As we move forward in this fight, we have to wield another weapon alongside our air strikes, our military, our counterterrorism work, and our diplomacy. And that's the power of our example," he said.

"We have to reject any attempt to stigmatize Muslim-Americans, and their enormous contributions to our country and our way of life."

Republican presidential front-runner Donald Trump has called for a temporary ban on Muslims entering the United States. Fellow Republican candidate Ted Cruz, a US senator from Texas, has called for heightened police scrutiny of neighborhoods with large Muslim populations.