The European Union is set to announce sanctions on Monday against three companies from Turkey, Jordan and Kazakhstan which are accused of violating a UN arms embargo on Libya, diplomats told AFP on condition of anonymity.
The EU has a naval mission operating in waters off Libya which is tasked with policing the embargo and collecting intelligence on violators.
Turkey is one of the biggest backers of the Government of National Accord (GNA) in Tripoli, which has been under attack from strongman Khalifa Haftar who runs a rival administration in the east.
"The sanctions are modest but significant. It's a signal," one of two diplomats who spoke to AFP said.
The targeting of a Turkish company risks inflaming already tense relations between Ankara and the EU following a recent flare-up in the eastern Mediterranean over oil and gas reserves.
The sanctions, which will see the companies blacklisted and their assets in the EU frozen, are expected to be endorsed by EU foreign ministers at a meeting on Monday in Brussels.
Libya has endured almost a decade of violent chaos since the 2011 NATO-backed uprising that toppled and killed veteran dictator Muammar Gaddafi.
EU member France has been accused in the past of supplying weapons to Haftar, who also has the support of Russia, Egypt and the United Arab Emirates.
French missiles were found at a base used by Haftar's forces last year, though the French defence ministry said they were decommissioned weapons which were being "temporarily stocked in a warehouse ahead of their destruction".
The Government of National Accord (GNA) in Tripoli is backed by Turkey and Qatar and UN officials have long warned that deliveries of foreign-made weapons to the country are undermining peace efforts there.