LONDON, Jan 7 (Reuters) - Britain provided support to the United States in its operation to seize a Russian-flagged oil tanker in the North Atlantic, the Ministry of Defence said on Wednesday.

The U.S. seized the tanker - which was being shadowed by a Russian submarine - on Wednesday, after pursuing it for more than two weeks across the Atlantic as part of Washington's efforts to block Venezuelan oil exports.

Britain said its armed forces gave "pre-planned operational support, including basing" following a U.S. request for assistance.

It said a military vessel provided support for the U.S. forces pursuing the tanker, and the Royal Air Force provided surveillance support from the air.

Defence Secretary John Healey said the operation targeted a vessel "with a nefarious history" linked to Russian and Iranian sanctions evasion networks.

“This action formed part of global efforts to crack down on sanctions busting,” he said in a statement.

He added that the U.S. was Britain's closest defence and security partner: "The depth of our defence relationship with the U.S. is an essential part of our security, and today's seamlessly executed operation shows just how well this works in practice."

The Bella-1 tanker, now renamed Marinera, is sanctioned by the U.S. under its counter-Iran sanctions, the British government said.

The MoD statement said the support was provided "in full compliance with international law".

(Reporting by William James, writing by Sam Tabahriti, editing by Paul Sandle and Kate Holton)