World powers see the Government of National Accord (GNA) as a crucial partner in tackling jihadists behind a string of deadly attacks in Libya as well as human traffickers exploiting the country's turmoil.
France's Jean-Marc Ayrault and Germany's Frank-Walter Steinmeier flew into the capital amid tight security for talks with the UN-backed cabinet which has set up operations at a naval base in the city.
The GNA is seeking "training for its police and military forces", Ayrault told journalists after the two envoys met prime minister-designate Fayez al-Sarraj.
It is the latest in a flurry of visits by European diplomats who had been absent since 2014 when EU member states closed their Tripoli embassies as fighting shook the North African nation.
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Their return was prompted by the arrival of the UN-backed prime minister on March 30 by sea with a naval escort, after a rival Tripoli authority closed the airspace to try to keep Sarraj out.
The visit comes two days before a crucial vote by the country's recognised parliament on whether to endorse the GNA, and ahead of the talks in Luxembourg.
Italy's Foreign Minister Paolo Gentiloni hailed the unity government as a "game changer" when he visited Tripoli on Tuesday.
The British, French and Spanish ambassadors flew in for talks two days later, saying they were working towards reopening their diplomatic missions there.
European nations are increasingly alarmed by the expansion of the Islamic State jihadist group in Libya, where it has established a new stronghold just 300 kilometres away from Italy across the Mediterranean.