A 1,000-strong "dark fleet" of rogue tankers evading sanctions has become a new target for the U.S. and Ukraine, according to a senior maritime intelligence analyst.

The founder of Russia's opposition Yabloko party, which wants a ceasefire in Ukraine, has said his party will keep campaigning despite the arrest of two senior figures, a move he said was meant to derail it before next year's parliamentary election.

At the core of the discussions in Berlin is the 20-point peace plan proposal presented to the US by Ukraine last week to counter an initial American plan which was seen as heavily favouring Russia.

Germany plans to deepen its defense cooperation with Ukraine, including for the first time the possibility of acquiring weapons and battlefield data from Kyiv, alongside a potential peace agreement under discussion in Berlin.

Russia targeted Ukraine's energy infrastructure with missile and drone strikes in another "massive attack" Friday night into Saturday morning, Ukrainian officials said.

The latest overnight attacks come as US envoy Steve Witkoff prepares to hold more talks with Ukraine's president.

Ukraine's internal security agency said the attack damaged and disabled a Russian Kilo-class submarine in the port city of Novorossiysk.