The U.N. nuclear watchdog pledged on Friday to investigate what it called serious U.S. accusations that Syria secretly built a nuclear reactor with North Korean help.

Syria, which denies the U.S. allegations, accused Washington of involvement in an Israeli attack on Syria in September that the United States says struck the site of a suspected atomic reactor.

Mohamed ElBaradei, director of the International Atomic Energy Agency, said the U.S. intelligence allegations against Syria would be investigated with due vigor.

"The Agency will treat this information with the seriousness it deserves and will investigate the veracity of the information," ElBaradei said.

He confirmed Washington had handed over information which said that a Syrian installation destroyed by an Israeli air strike in September was a not yet completed atomic reactor.

"According to this information, the reactor was not yet operational and no nuclear material had been introduced into it," he said in a statement.

But he said Syria would have been obliged under its non-proliferation safeguards agreement with the Vienna-based U.N. watchdog to inform it in advance of any planning and construction of a nuclear facility.

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