Airports in major U.S. cities were on high alert on Tuesday, with police out in force after at least 30 people were killed in bombings on Brussels airport and a rush-hour subway train, though officials said there was no specific threat to the United States.
U.S. President Barack Obama and Democratic presidential election contender Hillary Clinton vowed to do more to take on militants, while Republican presidential front-runner Donald Trump called for tighter border security and suggested U.S. intelligence services could use torture to head off future attacks.
The Obama administration was expected to tighten security at U.S. airports following the Brussels airport attack, which occurred in a public hall outside of the security check area.