The military deal will allow Ankara to deploy army trainers and equipment to the north African nation. Washington, which is on opposing sides with Russia in Libya's civil war, has decribed the move as "provocative."
Turkey's parliament on Saturday approved a military and security cooperation deal with Libya's internationally-recognized government, Turkey's state-run Anadolu news agency reported.
Already ratified by Libya's UN-backed Government of National Accord (GNA) two days earlier, Turkish lawmakers backed the agreement by 269 to 125 votes.
Ankara and Tripoli signed the security accord in November to boost cooperation between the two militaries. The pact will allow for a "quick reaction force" to be launched per Libya's request.
Turkey supports Libya's UN-backed administation, led by Fayez al-Serraj in its civil war against Khalifa Haftar's Libyan National Army, which controls territory in the east. Haftar is supported by Russia, Egypt and the United Arab Emirates.
Police and military responsibilities
According to Bloomberg, the pact allows for the training, consultancy, planning and material support for the establishment of a quick reaction force covering police and military responsibilities in the north African country. If required, it allows for a joint office of defense between the two countries.
The terms of the agreement are in violation of a UN arms embargo placed on Libya in 2011. However, Turkey has reportedly already sent military and combat supplies to the north African country. The UN has decried foreign involvement in Libya amid increased violence.
A US State Department official, speaking to the Reuters news agency on condition of anonymity, said Turkey's move was "unhelpful" and "provocative."
Turkish President Tayyip Erdogan said on Friday that Turkey could not remain silent over Russian-backed mercenaries backing Haftar and threatened to deploy troops to support the GNA. No formal request has been made yet.
Russia has expressed concerns over the possibility. The Kremlin said on Tuesday that Erdogan and Russian President Vladimir Putin are set to thrash out the feasibility of troop deployment to Libya next month during talks in Turkey.
To deploy troops in Libya, Erdogan first needs to file a separate motion for a vote by lawmakers following a request on Libya's part, according to Emrullah Isler, Erdogan's Libya envoy. However, he said, the Turkish president has ruled out deployment of combat troops.
Row with Greece over maritime pact
Along with the security agreement, Turkey and Libya are moving ahead with a contentious accord on maritime boundaries in the eastern Mediterranean, which has inflamed tensions with Greece.
Relations have been strained between Turkey and Greece due to Turkish drilling off the coast of Cyprus. The European Union has sanctioned Turkey in response to the drilling.
Libya's eastern neighbor Egypt denounced the pact as "illegal", while Greece has said the boundary agreement is invalid because it disregards the presence of the Greek island of Crete between Turkey and Libya.