Danish researchers have set sail for the North Pole to collect geological data, on a mission similar to Russia's trip earlier this month.
Denmark wants to determine how far Greenland extends north
The month-long Danish expedition will study the Lomonosov Ridge. Russia believes the underwater feature is linked to its territory.
Denmark will investigate the ridge to see if it is geologically connected to Greenland, a Danish territory.
Canada, Norway and the US also have claims in the Arctic.
The area is believed to be rich in oil and gas reserves, which global warming could make easier to extract as the ice melts.
"We'll go on until we have the best data. We'll have a lot of expeditions until 2014," Danish Science and Technology Minister Helge Sander told the BBC News website on Monday.
The Danish mission, called Lomrog (Lomonosov Ridge off Greenland), is supported by a Swedish icebreaker called Oden and a Russian nuclear icebreaker called 50 let Pobedy (50 Years of Victory), which was leased by Sweden.
Mr Sander said the Russians had simply "offered the best value". "The ship has a Russian crew - they'll do what we ask them," he added.
The research team - 45 specialists from Canada, Denmark and Sweden - plans to collect bathymetric, gravity and seismic data to map the seabed under the ice, the Danish science and technology ministry says.
The Danish mission was planned long before Russia's flag-planting on the Arctic seabed on 2 August, a ministry spokesman told the BBC News website.
The Danes set off on Sunday from Tromsoe in northern Norway. They will return to Norway's remote Svalbard islands on 17 September.
The lead researchers are Martin Jakobsson from Stockholm University in Sweden and Christian Marcussen from Denmark's GEUS (Geological Survey of Denmark and Greenland).
Mr Sander said "the fact that Russia and Canada have claims in the same area doesn't affect Denmark's right to claim".
"You can plant as many flags or send as many ministers as you want... In the end the important thing is to have the best data... We've put 230 million Danish kroner (£21m; $42m) into this North Pole project, for 2004 to 2010."
The North Pole seabed is not currently regarded as part of any single country's territory and is governed instead by complex international agreements.
Canada, Denmark and Russia are among many countries that have ratified the UN's Convention on the Law of the Sea, which allows a state sole exploitation rights over all natural resources within a 200-nautical mile (370km) zone extending from its coastline.
Beyond that, a state can claim the right to exploit a further 150 nautical miles of seabed if it can prove that its continental shelf extends that far.
Russia lodged a formal claim in 2001 but the UN's Commission on the Limits of the Continental Shelf told it to re-submit the claim.
On 2 August, Russian explorers planted a flag on the seabed 4,200m (14,000ft) below the pole.
The move drew derision from Canada, with Foreign Minister Peter MacKay likening it to tactics used in the 15th Century.
Canada and the US are also engaged in a dispute over the future of the Northwest Passage, the partially frozen waterway that links the Atlantic and Pacific oceans.
RUSSIA'S ARCTIC CLAIM
1) North Pole: Russia leaves its flag on the seabed, 4,000m (13,100ft) beneath the surface, as part of its claims for oil and gas reserves
2) Lomonosov Ridge: Russia argues that this underwater feature is an extension of its continental territory and is looking for evidence
3) 200-nautical mile (370km) line: Shows how far countries' agreed economic area extends beyond their coastline. Often set from outlying islands
4) Russian-claimed territory: The bid to claim a vast area is being closely watched by other countries. Some could follow suit