The U.S. officials, who spoke on condition of anonymity, said the United States has observed what appeared to be Russian special operations forces and drones at Sidi Barrani, about 60 miles (100 km) from the Egypt-Libya border, according to Reutersw.
Egyptian security sources offered more detail, describing a 22-member Russian special forces unit, but declined to discuss its mission. They added that Russia also used another Egyptian base farther east in Marsa Matrouh in early February.
The U.S. and diplomatic officials said any such Russian deployment might be part of a bid to support Libyan military commander Khalifa Haftar, who suffered a setback with an attack on March 3 by the Benghazi Defence Brigades (BDB) on oil ports controlled by his forces.
The Russian defense ministry did not immediately provide comment on Monday and Egypt denied the presence of any Russian contingent on its soil.
Read alsoRussian general seriously wounded in land mine blast in Syria – Kommersant"There is no foreign soldier from any foreign country on Egyptian soil. This is a matter of sovereignty," Egyptian army spokesman Tamer al-Rifai said.
Questions about Russia's role in north Africa coincide with growing concerns in Washington about Moscow's intentions in oil-rich Libya, which has become a patchwork of rival fiefdoms in the aftermath of a 2011 NATO-backed uprising against the late leader Muammar Gaddafi, who was a client of the former Soviet Union.
The U.N.-backed government in Tripoli is in a deadlock with Haftar, and Russian officials have met with both sides in recent months. Moscow appears prepared to back up its public diplomatic support for Haftar even though Western governments were already irked at Russia's intervention in Syria to prop up President Bashar al-Assad.
One U.S. intelligence official said Russia's aim in Libya appeared to be an effort to "regain a toe-hold where the Soviet Union once had an ally in Gaddafi."
"At the same time, as in Syria, they appear to be trying to limit their military involvement and apply enough to force some resolution but not enough to leave them owning the problem," the official added, speaking on the condition of anonymity.