Iraqi security officials said an explosion targeted a site used by the U.S. military next to Baghdad airport late Tuesday, one day before an expected visit by Iran’s president.

The expected visit by Iranian President Masoud Pezeshkian to Baghdad Wednesday would be his first official trip abroad since taking office.

Iraq’s security media cell said in a statement that an explosion was heard at 11 p.m. at the airport, in an area used by advisers to the U.S.-led international coalition.

The statement said Iraqi security forces were unable to determine the “type or causes of the explosion, and no party has claimed responsibility for it.” It added that the incident was under investigation and civilian air traffic continued as normal.