The US Environmental Protection Agency said on Tuesday it was reviewing its handling of a crisis over lead-contaminated drinking water in the Michigan city of Flint and acknowledged it did not respond fast enough.

"Our first priority is to make sure the water in Flint is safe, but we also must look at what the agency could have done differently," the agency said in a statement. An EPA spokeswoman confirmed the agency believed it did not act fast enough to address the problem.

Criticism of the state and federal response has grown in recent days over the crisis in Flint, a financially strapped city of just under 100,000 residents about 100 kilometers northwest of Detroit.