The pirates give their version of events from the ship
Somali pirates on board a hijacked ship are reported to have been involved in a shoot-out over what to do with the vessel's cargo of tanks and weapons.
An East African maritime group, which is monitoring the situation, told the BBC that three men were shot but the extent of their injuries was unclear.
Pirates seized the Ukrainian ship last week, demanding a $20m (£11m) ransom.
They dismissed the claim of infighting as "cheap propaganda", in a phone call to the BBC Somali Service.
"There has been no exchange of fire at all. We're in good shape," spokesman Sugule Ali told the BBC.
"This is cheap propaganda being spread by people not aware of our situation."
He added that the pirates were participating in dialogue, without going into detail.
"I am optimistic this can be resolved peacefully," he said.
In a separate development, the state-owned Malaysian shipping firm, MISC Berhad, said two of its ships had been recovered after it paid a ransom to pirates.
A spokesman said paying ransoms was against company policy, but had been necessary to obtain the release of its crew.
The hijacked Ukrainian ship, the Faina, is surrounded by international warships determined to stop its military cargo from falling into the wrong hands.
The US navy says its destroyers and cruisers are within 10 nautical miles (about 18km) of the ship.
Andrew Mwangura of the East African Seafarers' Association - who has been in contact with the vessel - told the BBC that two rival clans had been fighting over tactics.
He said radicals on board wanted to keep the shipment of 33 T-72 tanks and other weapons in Somalia while the moderates wanted "to back-pedal on the ransom issue".
Mr Mwangura said his main concern was the safety of the crew, and that the military activity in the area had unnerved the hijackers.
"We are asking the international community and the negotiators around that area to pull back - so they cool off," he told the BBC's Network Africa programme.
Earlier, the pirates said they would rather fight than surrender.
"I warn any military operation that, if we are attacked, we will defend ourselves until the last one of us dies," one of the hijackers told the BBC.
One of the ship's 21 crew is reported to have died from an illness on board.
The Faina is currently moored off Somalia's coast close to the town of Hoboyo. There have been conflicting reports of where the Faina and its cargo were destined.
Kenya has insisted that the shipment was destined for its military.
But other sources, including a US navy spokesman, said it was bound for the autonomous government of South Sudan, in possible contravention of a peace accord.
Somalia has been without a functioning central government for 17 years and has suffered continual civil strife, with rival armed clans and groups fighting for control.
The waters off its coast are considered to be some of the world's most dangerous - pirates have hijacked nearly 30 ships this year and attacked many more.
Even ships carrying food aid are often targeted, hampering the delivery of humanitarian supplies to the estimated three million Somalis in need of assistance.
A spokesman for the UN's World Food Programme said it supplies 90% of aid to Somalia by sea but that hijackings were increasing despite the number of naval forces patrolling the shipping lanes.