However, the spokesman said there was a "high possibility" that the ship had been located. French intelligence officials also believe they have found the ship in the same area, he said.
The Russian ambassador to Cape Verde, Alexander Karpushin, told Associated Press news agency that a Russian frigate was heading to the area but had no information on the Arctic Sea's location.
Russia's RIA news agency later quoted Mr Karpushin as saying that confirmation that the Arctic Sea had been spotted "400 nautical miles north of the island of Santo Antao... did not prove to be true".
Five Russian warships and other vessels have been searching the Atlantic for the vessel.
Carrying timber reportedly worth $1.8m (£1.1m), the Arctic Sea sailed from Finland and had been scheduled to dock in the Algerian port of Bejaia on 4 August.
The Arctic Sea went missing in mysterious circumstances last month
The crew reported being boarded by up to 10 armed men as the ship sailed through the Baltic Sea on 24 July, but the intruders were reported to have left the vessel on an inflatable boat after 12 hours.
There are also reports of the ship being attacked a second time off the Portuguese coast. However the ship's operators said they had no knowledge of the incident and Portugal said the ship was never in its territorial waters.
The last known contact with the crew was when the Arctic Sea reported to British maritime authorities as it passed through the Dover Strait.
On Friday, the European Union Commission spokesman Martin Selmayr said: "From information currently available it would seem that these acts, such as they have been reported, have nothing in common with 'traditional' acts of piracy or armed robbery at sea."
Nato was monitoring the situation due to the unusual nature and location of the attacks, but was not directly involved in the search.
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