German Chancellor Angela Merkel, Italian Prime Minister Giuseppe Conte and French President Emmanuel Macron said they "urge foreign actors to end their increasing interference and to fully respect the arms embargo."
"We are ready to consider the possible use of sanctions should breaches to the embargo at sea, on land or in the air continue," the joint statement added.
The trio said they expected EU foreign policy chief Josep Borrell to present his proposals to this effect.
They reaffirmed their commitment to the Irini operation that aims to stop smugglers from bringing weapons to Libya's warring factions by patrolling off its Mediterranean coast.
The leaders also said they backed UN efforts to mediate a lasting ceasefire in the North African country and urged it to explore all options, including a "potential demilitarization of certain areas."