(CNN) -- Naval forces from several countries were searching Tuesday for a British couple and their missing yacht, which may have been hijacked by pirates off the coast of Africa, military sources told CNN.
European Union anti-piracy forces may have spotted the missing vessel Tuesday, a spokesman told CNN.
"One of our helicopters spotted a yacht approximately 200 nautical miles from the Somali coast, towing two skiffs of the type normally used by pirates," Lt. Cmdr. Daniel Auwermann told CNN.
The yacht has not been identified, and the EU helicopter could not make contact with it, he said.
Paul and Rachel Chandler set off from the Seychelles for Tanzania on October 21, according to their blog. They have not been heard from since, but a distress beacon was activated October 23, according to naval officials.
International military forces are treating the case as a "potential hijacking," Lt. Ian Jones of Britain's Royal Navy told CNN. "We have no confirmation that anything has been pirated," he added.
There are many possibilities, he said, adding that he was aware of the reports of piracy but that hijacking was "far from certain."
The weather in the area is quite good, he said.
Before setting off, the Chandlers said that the journey could take as long as two weeks and that they would be out of contact for part of the voyage.
"We probably won't have satellite phone coverage until we're fairly close to the African coast, so we may be out of touch for some time," they wrote before setting off in the Lynn Rival, a 38-foot yacht.
Britain's Foreign Office issued a statement saying it is "extremely concerned for their safety," while pointing out that it had not confirmed reports they were taken captive.
Pirates have been active off the east coast of Africa in the past several years, operating out of lawless Somalia. Two vessels were attacked the day after the Chandlers set sail. One of them -- a cargo ship -- was successfully boarded and seized off the Seychelles, while the other fought off its attackers near the Kenyan coast.
Attacks in the region have significantly increased this year, according to the International Maritime Bureau, which monitors shipping crimes. But successful attacks have decreased as a result of a strong presence of international monitors.
The first nine months of this year have seen more pirate attacks than all of last year, the bureau reported October 21.
From January 1 until September 30, pirates worldwide mounted 306 attacks, compared with 293 in all of 2008, it said. More than half of this year's attacks were carried out by suspected Somali pirates off the east coast of Somalia and in the Gulf of Aden, a major shipping route between Yemen and Somalia.
Out of those attacks, Somali pirates successfully hijacked 32 vessels and took 533 hostages. Eight people were wounded, four were killed and one is missing, the bureau said.
CNN's Adam S. Levine contributed to this report.