"Libya: EU strongly concerned about Turkey's decision to intervene in the conflict. Supporting those who are fighting there will only further destabilise the country & wider region. UN arms embargo must be respected by all", Stano wrote on Twitter.
He added that peaceful settlement was still the only way out of the crisis.
"The EU reiterates its firm conviction that there is no military solution to the Libyan crisis ... The EU will maintain an active engagement in support of all de-escalatory measures and steps leading to an effective ceasefire and the resumption of political negotiations", the spokesman said in a statement posted on the European External Action Service website.
The statement comes after the Turkish parliament approved President Recep Tayyip Erdogan's initiative to deploy the country's armed forces in Libya following an official request by the GNA which is currently trying to fend off an offensive by the Libyan National Army led by Khalifa Haftar.
After the ouster and assassination of then-Libyan leader Muammar Gaddafi in 2011, the country was plunged into a brutal civil war. Today, Libya is divided between two centres of power — an elected parliament in the country's east, supported by Haftar's forces and the UN-backed GNA in the west.