Iran said on Wednesday that unidentified foreign planes violated its air space six times as the country kicked off its biggest ever air defense drill but that the intruders were intercepted and forced back by Iranian jets.

The remarks by Gen. Hamid Arjangi, a spokesman for the exercise, were the first Iranian claim of an intrusion. Initially, he had only said that foreign reconnaissance planes had approached Iran's air space.

Arjangi said Iran's radar stations and observation posts picked up on the planes entering Iranian air space during the five-day drill, which started Tuesday.

"There were six cases of intrusion by unidentified planes into the country," Arjangi was quoted as saying by the official IRNA news agency. "In all six cases, Air Force jet fighters took off and carried out interception operations ... artillery systems were alerted, targets were identified and necessary warnings were given."

The Iranian exercise is meant to showcase the country's capabilities in defending its nuclear facilities from possible attack.

It followed an announcement by the Iranian Air Force saying its troops earlier this year conducted an exercise at several facilities — from the uranium enrichment plant at Natanz, the under-construction enrichment site at Fordo, to the nuclear conversion facility near Isfahan and the Bushehr nuclear power plant.

Arjangi said thousands of watchers have been stationed along 4,400 miles (7,000 kilometers) of Iran's border, equipped with sophisticated communication systems capable of countering enemy jamming to transfer data to control command centers. He did not specify whether the figure, which is only a segment of the total Iranian borderline, referred to that in the Persian Gulf.

Gen. Ahmad Mighani, head of an air force unit in charge of responding to threats to Iran's air space, said Tuesday the war games seek to "upgrade the combat preparedness" of the country's air defense system.

The United States and its European allies accuse Iran of embarking on a nuclear weapons program. Iran denies the charge and insists the program is only for peaceful purposes.

Israel has not ruled out military action to stop Iran from obtaining nuclear weapons.

Iran is expected to unveil a locally made radar system with a range of some 1,800 miles (2,900 kilometers) during the drill

Iran's armed forces conduct several war games every year and frequently unveil new weapons and military systems during those exercises.

There was no immediate comment from the U.S. Navy's Bahrain-based 5th Fleet.