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 U.S. has agreed to provide unspecified security guarantees to Ukraine as part of a peace deal to end Russia's nearly four-year war, and more talks are likely this weekend, U.S. officials said Monday following the latest discussions with Ukrainian President Volodymyr Zelenskyy in Berlin.

By Andreas Rinke, Tom Balmforth and Steve Holland BERLIN/WASHINGTON, Dec 15 (Reuters) - U.S. negotiators have offered to provide NATO-style security guarantees for Kyiv as U.S. and European negotiators reported progress in talks on Monday to end the war with Russia,

Two U.S. officials who spoke on the condition of anonymity said the arrangement would be similar to the NATO mutual defense agreement. But crucial details remain unsettled as negotiators seek a deal that Russia will approve.

Ukraine has relinquished its ambition of joining the NATO military alliance in exchange for Western security guarantees as a compromise to end the war with Russia, President Volodymyr Zelenskyy said ahead of talks with U.S. envoys in Berlin.

U.S. peace negotiators have told Ukraine during peace talks in Berlin that it must agree to withdraw its forces from the eastern Donetsk region as part of any deal to end the nearly four-year-old war,

U.S. officials have indicated that Putin is open to Ukraine joining the European Union, as well as other security guarantees to Ukraine.