Once-secret U.S. diplomatic cables have revealed concerns by U.S. officials that Islamic militants might get access to Pakistani nuclear material, according to a French newspaper report.

The revelation was published Tuesday night on the website of the newspaper Le Monde, one of the dailies that document-discloser WikiLeaks provided some of its more than 250,000 leaked American diplomatic files to.

The newspaper says in the cable traffic through Islamabad that President Barack Obama reportedly confided Pakistan was his “private nightmare.”

A February 2009 memo from then-U.S. Ambassador Anne Patterson in Islamabad said “our main worry” wasn’t that an entire bomb might be stolen, but that a worker at a Pakistani nuclear site “might bring out enough fissile material to build a bomb.”

Le Monde also reported that in 2007 Pakistan had agreed “in principle” to an operation to remove highly enriched uranium from a Pakistani nuclear reactor, but it was never carried out.

Pakistan said Monday it refused the operation because its own nuclear security would prevent the material from getting into the wrong hands.

If the Pakistani press were to find out about such a withdrawal of highly enriched uranium it would cast the operation as a U.S. seizure of Pakistan’s nuclear arsenal, one Pakistani official told U.S. embassy staff.

The newspaper published the comments in a French translation. The Associated Press requested the original in English but it was not immediately available.

U.S. Secretary of State Hillary Rodham Clinton has said that WikiLeaks acted illegally in posting the leaked documents. Officials around the world have said the disclosure jeopardizes national security, diplomats, intelligence assets and relationships between foreign governments.

Five international media organizations received the documents in advance. WikiLeaks is also slowly posting all the material on its own website.

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