News agency Reuters has been forced to admit that footage it released last week purportedly showing Russian submersibles on the seabed of the North Pole actually came from the movie Titanic.

The images were reproduced around the world - including by the Guardian and Guardian Unlimited - alongside the story of Russia planting its flag below the North Pole on Thursday last week.

But it has now emerged that the footage actually showed two Finnish-made Mir submersibles that were employed on location filming at the scene of the wreck of the RMS Titanic ship in the north Atlantic some 10 years ago.

This footage was used in sequences in James Cameron's 1997 blockbuster about the 1912 disaster.

The mistake was only revealed after a 13-year-old Finnish schoolboy contacted a local newspaper to tell them the images looked identical to those used in the movie.

Reuters has admitted that it took the images from Russian state television channel RTR and wrongly captioned them as file footage originating from the Arctic.

RTR had also used the footage to illustrate stories about the North Pole expedition, but it is thought as library footage, and it never claimed it was actually of the flag-planting.

The pictures were first broadcast by RTR when the Russians were still several hours away from the North Pole.

Reuters distributed a package of clips that included the scenes from Titanic, alongside computer animations and footage of ships on the surface at the North Pole.

In its piece on the subject, two of the four Reuters pictures were from the Titanic filming.

Reuters has now apologised for the error and has made changes to its video material on the expedition, with captions denoting the various origins of the file footage used.

In a statement, Reuters said: "On August 2, 2007 in a TV story about two Russian submersibles planting a flag on the seabed under the North Pole, we used file shots of MIR submersibles as part of this story.

"Reuters mistakenly identified this file footage as originating from the Arctic, and not the North Atlantic where the footage was shot.

"This footage was taken during the search for the Titanic and copyright is held by Russian State broadcaster RTR.

"This location error was corrected as soon as it was brought to our attention. A still image of the submersibles was also taken from the footage and put out on the Reuters photo wire. The caption has been corrected."

The incident is doubly embarrassing for the agency since it follows a case in August last year in which it published an image by a freelancer of Israeli bombings in Lebanon that had been dramatised using photo manipulation, with the addition of smoke rising from allegedly burning buildings.

After that gaffe, Reuters promised to tighten up its controls on material being put out in its name.

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