Washington/Nairobi - A hijacked lifeboat with the captain of a US cargo ship held hostage was nearing the Somali shore Saturday after talks with the pirates collapsed and they fired on a US Navy vessel.

The developments escalated concern for the fate of captain Richard Phillips, the US captain of the Maersk Alabama who has been held by the pirates off the Horn of Africa since Wednesday

Somali pirates obtained fuel for their hijacked lifeboat and were moving within 35 kilometres of Somalia's shore late Saturday with Phillips on board, ABC news and CNN reported.

In Washington, Pentagon spokesman Major Stewart Upton told dpa he could share no information about an agreement to release Phillips or the failed attempt by a US patrol craft to rescue him. He indicated that serious concern about Phillips' fate meant the US Defence Department could release no information.

Three-way negotiations that involved Somali clan elders apparently collapsed when the Americans insisted that the pirates be handed over to Somali authorities, the New York Times reported. The Times cited Abdul Aziz Aw Mahamoud, a district commissioner in the semi- autonomous region of Puntland in northeastern Somalia, as the source of the information.

The US Navy is reluctant to intervene out of concern for Phillips' life. On Friday, French naval forces stormed a yacht taken in the region last weekend. Two pirates and one hostage were killed in the raid, and the French are investigating to find out who fired the bullet that killed the captain of the yacht.

In another hijacking on Saturday, pirates took an Italian-operated tugboat, the Buccaneer, with 16 people on board in the Gulf of Aden, including Italians, Romanians and a Croatian.

The 17,000-tonne Alabama, carrying food aid for three countries, steamed into the port of Mombasa, Kenya, late Saturday, where it has been declared a crime scene by US investigators, John Reinhart, chief executive of the Alabama's Maersk Line, told reporters in Norfolk, Virginia.

The crew must stay on board during the investigation, he said.

"Our first and only priority as we go into the coming days" is the safe release of Phillips, Reinhart said.

The crew re-gained control of the Alabama on Wednesday after hijackers tried to take the wheel. They steered toward Mombasa after the USS Bainbridge took its place in the standoff with the lifeboat.

The father of Sean Murphy, the Alabama's first mate who took command when Phillips was taken off the ship, told CNN that the crew was "very disappointed" they had to leave the captain behind.

"My son indicated that the worst part was for him and the rest of the crew to leave behind captain Phillips," Murphy's father said in broadcast remarks.

The FBI has instructed Murphy and other crew members not to discuss details of the hijacking and kidnapping with family members. Each has been given a phone in Mombasa to contact their family, but with limitations on what they can discuss, Reinhart said.

In shouted interviews with ABC and CNN in Mombasa, crew members indicated that some of them had hidden and then attacked the pirates after the Alabama had been boarded. One of the crew stabbed a pirate in the hand.

Phillips apparently gave himself up as hostage to get the four heavily-armed pirates off the ship, according to their comments. But Reinhart dismissed the suggestion that he surrendered as "speculation."

Over the past two days, the USS Bainbridge and the fuel-less lifeboat were reported in a standoff 500 kilometres offshore on the high seas of the Indian Ocean. It was not clear where the kidnappers obtained fuel.

Phillips, who is being celebrated as a hero in US newspapers, tried to escape on Thursday by jumping into the water, but he was hauled back by the kidnappers under gunfire within sight of the Bainbridge and was later bound to prevent another attempt.

On Saturday, a US Navy patrol boat launched from the Bainbridge tried to approach the lifeboat but was fired on, according to media reports. The crew retreated, to avoid endangering Phillips.

Initial reports said the boat had intended to rescue Phillips, but later reports said the officers on board were trying to make contact or reconnoiter the situation.

Phillips is one of an estimated 200 hostages being held by Somali pirates, who attacked more than 165 ships since last year, according to the US Fifth Fleet in Bahrain. Some ships have been exchanged for millions of dollars in ransom paid by the shipping lines or their insurers.

Ship crews are unarmed, but some ships have added barbed wire to protect access. European, the US and other governments have launched a coordinated effort to patrol the waters.

Asked what kind of person Phillips was, Reinhart quipped: "He's a mariner. He's one of the best."

US President Barack Obama was reported to be following the situation closely.