By Barbara Starr CNN Pentagon Correspondent

(CNN) -- A US Navy EP-3 and P-8 aircraft were threatened with a potential shoot down over the weekend by Iran as they were flying in the northern Persian Gulf, according to initial reports, a US defense official said.

The aircraft were flying in international airspace but "near Iranian airspace."

The Iranians made a radio call to both planes warning them not to enter Iranian airspace and risk being shot down, the official said. The US aircraft never entered Iranian airspace and proceeded without incident.

The Iranians threatened to launch missiles to shoot down the aircraft, as part of the threat.

Also, senior US military officials are increasingly trying to assess whether the number of incidents with the Iranians have actually increased or whether more incidents are simply being reported by US Naval commanders in the region because of the sensitivity to Iranian incidents.

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