Washington (BBN)-Islamic State militants have set up training camps in eastern Libya, the head of the US Africa command says.
Gen David Rodriguez said there could be "a couple of hundred'' IS fighters undergoing training at the sites.
He said the camps were at a very early stage, but the US was watching them "carefully to see how it develops", reports BBC.
Libya has been in turmoil since Muammar Gaddafi was overthrown in 2011, with various tribes, militias and political factions fighting for power.
Several Islamist groups are competing for power in the east of the country, with some militants recently declaring allegiance to IS.
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Speaking in Washington on Wednesday, Gen Rodriguez said it was not yet clear how closely aligned the trainees were with IS.
"It's mainly about people coming for training and logistics support right now, for training sites," he said. "Right now it's just small and very nascent and we just have to see how it goes."
Correspondents say that in the aftermath of the revolution that ousted Gaddafi, many rebel fighters left to fight with militant groups in Syria, and some are believed to have returned home.
The elected government has lost Libya's three main cities amid the political crisis.
Benghazi, the country's second city, is in the hands of Islamist fighters, and the internationally recognised parliament is now based in the coastal town of Tobruk in the east.
The US has been leading an international coalition conducting air strikes against IS in Iraq and Syria in recent months.
BBN/AS-04Dec14-1:10pm (BST)