The head of the UN nuclear monitoring agency has criticised the US for withholding intelligence information that it says showed the construction a nuclear reactor in Syria.

Mohamed ElBaradei, head of the International Atomic Energy Agency (IAEA), on Friday also hit out at Israel for bombing the site before inspectors could investigate.

ElBaradei "deplores the fact" that the information was not immediately passed onto the Vienna-based watchdog in accordance with the guidelines of the nuclear Non-Proliferation Treaty (NPT), the IAEA said in a statement.

"Under the NPT, the agency has a responsibility to verify any proliferation allegations in a non-nuclear weapon state party to the NPT," the agency said.

North Korean help

ElBaradei also the agency would investigate the claims that Syria was building a secret nuclear reactor with North Korea's help.

In depth

Full text: US statement Full text: Syrian statement Interview: Seymour Hersh

Washington alleged that the facility had a military purpose until Israel destroyed it in a bombing raid last September.

The watchdog was critical of both the US and Israel for their handling of the matter.

"In light of the above, the director general views the unilateral military action by Israel as undermining the due process of verification that is at the heart of the non-proliferation regime," it added.

The agency said it was taking seriously the allegations that were passed on by the United States on Thursday and will investigate the findings.

"[We] will treat this information with the seriousness it deserves and will investigate the veracity of the information," it said.

"Syria has an obligation under its safeguards agreement with the IAEA to report the planning and construction of any nuclear facility."