A French military operation to free a yacht hijacked by Somali pirates backfired yesterday when one of the hostages was killed, highlighting the perils facing US forces trying to free an American seaman being held captive in a parallel pirate standoff.

Despite the rescue of his four fellow hostages, including his three-year-old son, Florent Lemaçon was shot dead on board the Tanit during the raid by elite French forces. Two pirates also died, and three others were taken prisoner, said the French defence minister, Herve Morin.

Standing by the commando-style tactics, the French president Nicolas Sarkozy's office confirmed "France's determination not to give into blackmail, and to defeat the pirates".

However, Morin later said that, in a break with usual French policy, a ransom had been offered to the pirates, who hijacked the Tanit last weekend as it sailed towards Zanzibar. He said Sarkozy had given the order to attack after negotiations had broken down and the pirates threatened to execute the hostages.

"Of course we offered all we could offer ... we even offered them a ransom," said Morin, declining to name the sum proposed. "All these things were permanently and consistently refused." He said France had also suggested "exchanging" Colin, the child, and his mother, Chloe, for an officer, but that had also been rejected.

Military sources last night said it was unclear whether Lemaçon, the owner of the yacht, had been killed accidentally or whether he had been murdered. General Jean-Louis Georgelin, the army chief, said the 28-year-old had been shot inside the yacht during an exchange of fire between French forces and the pirates.

Officials expressed exasperation at the determination of the Tanit's crew to persist with their expedition despite the parlous security situation in the region, saying the couple had been "strongly warned" about their adventure by the navy .

Amid accusations the couple, who set off from Brittany last year, had behaved irresponsibly, Lemaçon's father, Francis, last week defended their actions. "They are experienced sailors and certainly not irresponsible. They followed the advice they were given, took the less dangerous route and were in constant contact with the French forces," he told the Ouest France newspaper.

France has taken a robust approach to the piracy scourge threatening the world's shipping through the vital Gulf of Aden-Indian Ocean conduit. Twice it has sought to make pirates pay for their actions; firstly last April, by pursuing the bandits on land through Somalia, and then in September by storming a seized French yacht.

But the unfortunate outcome of yesterday's operation underscored the formidable difficulties facing taskforces policing the treacherous waters off east Africa.

In particular, it will focus attention on the US military as it confronts a hostage crisis unfolding further north off the Horn of Africa, where a US seaman is being held by four gunmen adrift in a lifeboat.

Captain Richard Phillips offered himself up as a hostage to persuade the armed bandits to leave his ship, the Maersk Alabama, which was seized on Wednesday. The US quickly dispatched a destroyer, the USS Bainbridge, to the scene. The warship is prowling several hundred yards away from the drifting launch.

At one point early yesterday, Phillips tried to escape by swimming to the destroyer. The four pirates quickly jumped in and hauled him back aboard. Later, allies of the pirates told Reuters they wanted $2m (£1.36m) for their captive.

After a winter lull, the epidemic of piracy in the Indian Ocean has rapidly re-emerged in recent days. Various gangs along Somalia's coast are holding 18 foreign ships – including five taken this week – and more than 250 hostages. Success last year, when they netted tens of millions of pounds in ransoms, has allowed them to invest in new boats and equipment, enabling the pirates to attack far out to sea.

The hijacking of the Alabama is believed the first pirate attack on an American-flagged merchant ship in 200 years. Last night, a pirate source told Reuters that associates were heading towards the scene of the standoff on a captive German vessel with foreign hostages still on board to act as human shields.

"Knowing that the Americans will not destroy this German ship and its foreign crew, they [the approaching pirates] hope they can meet their friends on the lifeboat," the pirate said.

But with at least two other US warships approaching, it was unclear whether the pirates would dare, or be allowed, to get near the lifeboat, which has run out of fuel.

"Other pirates want to come and help their friends, but that would be like sentencing themselves to death," said Andrew Mwangura, co-ordinator of the East African Seafarers' Assistance Programme, which monitors the region's seas.

Some observers believe the stalemate can still be resolved without ransom or bloodshed. Mwangura said he expected Phillips would be released in exchange for guaranteed safe passage back to Somalia for the gunmen. "I think this will be resolved in the next day or two," he said.

The pirates may, however, have enough resources in the lifeboat to last some time longer than that. Joseph Murphy, a professor at the Massachusetts Maritime Academy, and whose son Shane is second in command of the Alabama, said the 8.5m(27ft) lifeboat was likely to have been stocked with enough food and water to last 34 people for 10 days.

The Tanit blog

Extracts from the blog Chloe Lemaçon wrote during the family's journey:

First post, November 2007 "... We want to travel as close as possible to nature ... we just want to show Colin that you don't really need any of that ... to be happy."

July 2008 "For us, leaving is just about living differently. We don't want to become rich and famous. We don't want to lock ourselves in the everyday life of the west ..."

January 12 2009 "There's still the problem of piracy. We have read up on it and think the subject is hyped up by the media. It's true there is a risk, but no higher than in Venezuela, for example"

March 5 "The night is calm, the wind from the north has weakened. In the early hours the sea is beautiful ... we caught our fourth barracuda so Flo made us fried fish with buckwheat ..."

Final post, March 20 "... We are right in the middle of the piracy danger zone ... however nothing to show for it ... [a French navy commander] advises us to stay off the commercial shipping routes ... it's rather nice to have this contact with France in the middle of the sea, far from home!"