Turkey has also said it could deploy troops to Libya if the GNA makes such a request. The GNA has been fighting a months-long offensive by Khalifa Haftar's forces based in the east of the country. Haftar's forces have received support from Russia, Egypt, Jordan and the United Arab Emirates.
Speaking in the northern province of Kocaeli, Erdogan said Turkey had recently provided "very serious" support to the GNA, adding Libya was a country Turkey would support "with its life". "They are supporting an illegal warlord, who is the pawn of certain nations, instead of the U.N.-recognised government," Erdogan said, in an apparent reference to Haftar and the countries who support him.
"If necessary, we will increase the military aspect of our support to Libya, and evaluate all our options, from the ground, air and sea," he said. Speaking before Erdogan, Defence Minister Hulusi Akar said Turkey will stand by Libya's government until peace, stability and security are established in the country.
Last month, Turkey and the GNA signed an accord to boost military cooperation and a separate deal on maritime boundaries, which has enraged Greece. Ankara and Athens have been at odds over hydrocarbon resources off the coast of the divided island of Cyprus.
While Greece has said the accord violates international law, Turkey has rejected those accusations, saying it aims to protect its rights in the eastern Mediterranean. On Sunday, Erdogan said Turkey will "absolutely" not turn back from its agreements with Libya.
"Nobody should come to us with attempts to exclude us, trap us in our own shores or steal our economic interests," Erdogan said. "We have no intention of starting conflicts with anyone for no reason, or robbing anyone of their rights," he said.
"Those who oppose us have no sense of rights, law, justice, ethics or mercy," Erdogan said, referring to Greece, Israel and Egypt, who have opposed the maritime accord.
In an interview with Greek daily To Vima on Sunday, Foreign Minister Mevlut Cavusoglu said the accord with Libya was in line with international law, adding Ankara may consider granting exploration licenses in areas determined by Turkey and Libya.
"It would be the exercise of our sovereign rights in our continental shelf in the region," Cavusoglu said. "The exercise of our sovereign rights also and naturally includes our right to deploy research vessels in the area," he was cited as saying.
In a first reaction from the United States on the agreement, a senior U.S. State Department official said the maritime accord was "unhelpful" and "provocative."