A US Navy destroyer has made visual contact with a Ukrainian ship which was seized by pirates last week and is now moored off the Somali coast.
There is no indication that the USS Howard intends to approach the ship, which is carrying 33 battle tanks destined for Kenya's government.
The pirates' ransom demand for the ship and its 21 crew has fallen from $35m to $20m (£10.9m), their spokesman said.
A man on the ship also told the BBC that one of the crew members had died.
The man, who the pirates said was the captain of the MV Faina, was speaking via a satellite phone handed to him by one of the pirates.
He said the dead sailor was Russian and had died as the result of an illness. The report could not be confirmed by independent sources.
He also said the other crew members were fine and that he could see three ships about a mile away, including one carrying a US flag.
In an earlier interview with the BBC, a spokesman for the US Navy's 5th Fleet, Lt Nathan Christensen, said the USS Howard was within 8km (5 miles) from the Ukrainian vessel, but refused to say whether an intervention was likely.
"The USS Howard… [is] currently on station, in visual contact and is monitoring the situation there," he said.
"The motor vessel is anchored off the Somali coast, near the town of Hobyo, along with, actually, a couple of other pirated vessels that are also anchored in that location."
Lt Christensen said the USS Howard had been in contact with MV Faina using VHF radio, and that negotiations were continuing between the pirates and its owners.
He said the ship's cargo of Russian-made T72 battle tanks made it a particularly worrying situation.
"We're concerned that this might end up in the wrong hands, such as terrorists or violence extremists," he said.
One of the pirates, Sugule Ali, claiming to be speaking on their behalf, later told reporters via satellite phone that they wanted a ransom and "nothing else".
"We need $20m for the safe release of the ship and the crew," he told the Associated Press news agency.
"If we are attacked, we will defend ourselves until the last one of us dies."
On Saturday, another of the pirates, Januna Ali Jama, told the BBC they would not release the MV Faina unless a ransom of $35m (£19m) was paid.
Later, a spokesman for the Kenyan government said they had not received any credible demands for a ransom to release the ship.
The waters off the coast of Somalia are considered some of the world's most dangerous.
Ukraine has confirmed that the tanks and "a substantial quantity of ammunition" were aboard the MV Faina.
The ship had a crew of 21 and was sailing towards the Kenyan port of Mombasa.
Authorities in Somalia's semi-autonomous region of Puntland say they are powerless to confront the pirates, who regularly hold ships for ransom at the port of Eyl.
The USS Howard is one of several vessels in the area
Last week, France circulated a draft UN resolution urging states to deploy naval vessels and aircraft to combat such piracy.
France, which has troops in nearby Djibouti and also participates in a multi-national naval force patrol in the area, has intervened twice to release French sailors kidnapped by pirates.
Commandos freed two people whose boat was hijacked in the Gulf of Aden earlier this month and in April, six arrested pirates were handed over to the French authorities for trial.
Somalia has been without a functioning central government for 17 years and has suffered from continual civil strife.