One of the sources, who asked not to be named, told AFP the sanctions comprise "a ban on travelling in the European Union and a freeze on assets in the EU, which could be effective as it seems they have assets in Malta."
"The sanctions will come into effect after they are published in the EU's Official Journal on Friday," the source said.
The source did not identify those involved but said "it is the same three names we have been talking about."
A European diplomatic source told AFP recently that EU sanctions would target the Tripoli government's prime minister Khalifa Ghweil, the head of the General National Congress Nuri Abu Sahmein, and Aguila Saleh, speaker of the Tobruk-based parliament.
US officials would not immediately say whether Washington would follow suit in imposing sanctions, but a State Department spokesman said "those trying to sabotage Libya's future will be held accountable by the Libyan people and the international community for their actions."
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EU foreign affairs chief Federica Mogherini said earlier this month the 28-nation bloc was readying sanctions amid increasing frustration that Libya's UN-backed unity government set up in December was being prevented from taking office in the capital Tripoli.
On Wednesday, prime minister designate Fayez al-Sarraj arrived in Tripoli by sea from Tunisia, along with several members of his cabinet, but the authorities in the capital told him bluntly to leave or "hand himself in."
"Those who entered illegally and secretly must surrender or turn back," Ghweil said in a televised address. "We won't leave Tripoli as long as we are not sure of the fate of our homeland."
Libya descended into chaos after the 2011 NATO-backed ouster of longtime dictator Moamer Kadhafi, allowing extremists including the Islamic State group to gain a foothold in the once oil-rich country.
Since 2014, Libya has had two rival administrations after militia groups forced the government from Tripoli to seek safety in Tobruk in the east.
The UN-brokered agreement in December was to set up a new unity government but lawmakers in Tobruk initially rejected it, only to then change their minds.