A spokesman for the Libyan anti-Islamist movement Operation Dignity denied on Wednesday that Egyptian airplanes took part in fighting in Benghazi.
Mohamed El-Hagazi added that Islamist sites in Benghazi were hit by Libya's Air Force.
Egypt also denied that its military airplanes bombed Islamic militia sites in war-stricken Benghazi.
Presidential spokesman Alaa Youssef told Al-Ahram's Arabic news website that the news was "completely untrue".
Speaking with Ahram Online, Foreign Ministry spokesman Badr Abdel-Aty also denied an AP report published earlier Wednesday stating that Egyptian warplanes were attacking Islamists in war-stricken Benghazi.
The AP report quoted two Egyptian officials who requested anonymity as they were not authorised to speak to the media.
"Libyan lawmaker Tareq Al-Jorushi confirmed...that Egyptian warplanes were taking part in the ongoing operation in Benghazi, but added that they were being flown by Libyan pilots," AP said.
Benghazi has witnessed recent deadly fighting between Islamist militants and the country's army.
Libyan Interior Minister Omar Al-Sanky and his Egyptian counterpart Mohamed Ibrahim agreed on 9 October that Egypt would train Libya's security forces to help fight "terrorism".
Ex-army general Khalifa Haftar launched Operation Dignity against Islamists in Libya to regain control over Libyan cities that fell to Islamist militias. The Libyan and Egyptian governments have expressed their support to him.
Libya has been engulfed by insurgencies since the 2011 toppling of long-time leader Muammar Gaddafi, with interim authorities fighting Islamist-led militias that have seized the capital Tripoli and named a rival government.
Egypt has been concerned over a possible spill out of violence from neighbouring Libya, especially over militants crossing the border.