BRUSSELS, April 25 (Reuters) - The European Commission's next sanctions package is expected to propose restrictions on Russian liquefied natural gas (LNG) for the first time, including a ban on trans-shipments in the EU and measures on three Russian LNG projects, three EU sources said.

The Commission is in the final stages of ironing out its proposal and is engaged in informal talks with member states this week. The Commission declined to comment.

The EU announced a ban on Russian seaborne oil imports soon after Russia's invasion of Ukraine in February 2022, but the bloc has stopped short of prohibiting LNG, despite repeated calls by Baltic states and Poland.

Imports of Russian LNG to Europe have jumped since the war began. EU statistics and Reuters calculations show the rise in LNG has pushed the share of Russian gas in EU supply back up to around 15% after pipeline imports from Russia's state-owned Gazprom (GAZP.MM), plunged to 8.7% from 37% of EU gas supply.

Belgium, France, and Spain have become the biggest importers. A transshipment involves moving the LNG from one vessel to another ship that then sails onto its final destination. The transfers are usually done in port areas.

The other measure would be to impose sanctions on three Russian LNG projects - Arctic LNG 2, Ust Luga and Murmansk - that are not yet operational.

The details are still being discussed, but one source said the Commission proposal would be finalised by the end of next week.

The sources said there would likely be more support to sanction the projects than to ban transshipments when the final proposal is formally presented to EU member states.

(Reporting by Julia Payne, Kate Abnett and Jan Strupczewski; Editing by Kirsten Donovan and Sharon Singleton)