Israeli missiles have hit a site in Iran, ABC News reported late on Thursday, citing a US official, while Iranian state media reported an explosion in the center of the country, days after Iran launched a retaliatory drone strike on Israel.

Iran’s Fars news agency said an explosion was heard at an airport in the central city of Isfahan but the cause was not immediately known. Iran suspended flights over the cities of Isfahan, Shiraz and Tehran, state media reported.

Several Iranian nuclear sites are located in Isfahan province, including Natanz, centerpiece of Iran’s uranium enrichment program. Isfahan, Isome 350 kilometers (215 miles) south of Iran’s capital, Tehran, is also home to a major air base for the Iranian military.

Tehran’s Imam Khomeini International Airport was closed to all flights until 7:00 GMT, according to a notice to airmen posted on a US Federal Aviation Administration database.

Iran’s government offered no immediate comment. The Israeli military did not immediately respond to a request for comment

Some Emirates and Flydubai flights that were flying over Iran early on Friday made sudden sharp turns away from the airspace, according to flight paths shown on tracking website Flightradar24.

Israel had said it would retaliate against Iran’s weekend attack, which involved hundreds of drones and missiles in retaliation for a suspected Israeli strike on its embassy compound in Syria. Most of the Iranian drones and missiles were downed before reaching Israeli territory.

Analysts and observers have been raising concerns about the risks of the Israel-Gaza conflict spreading into the rest of the region.

Iran told the United Nations Security Council on Thursday that Israel “must be compelled to stop any further military adventurism against our interests” as the UN secretary-general warned that the Middle East was in a “moment of maximum peril.”