Abdullahi Mohamed told The Associated Press that he has ties with the gang holding the family — a Danish couple with three children, aged 12 to 16.
Most hostages captured in the pirate-infested waters off East Africa are professional sailors. Pirates rarely capture families and children, but a 3-year-old boy was aboard a French yacht seized in 2009. His father was killed in the rescue operation by French navy commandos. Two pirates were killed and four French citizens were freed, including the child.
The Danish family was captured along with two adult crew members, also Danes, when their sailboat was seized by pirates Thursday, the Danish government said.
Mohamed said that any attack against the pirates would result in the deaths of the hostages, and he referred to the killings last week of four American hostages captured by pirates on their yacht.
Mohamed has provided reliable information to AP in the past.
Just days before the hijacking, the family wrote on a travel blog that it was in daily contact with anti-piracy forces and had prepared a "piracy plan" in case of an attack.
Blog postings chronicling the family's round-the-world journey showed it entered the area well aware that the American yacht had been hijacked by pirates but comforted by the presence of counter-piracy forces.
"Of course, we talked quite a lot about it but this is far over thousands of kilometers (miles) away and the Arabian Sea that we sail in is the size of Europe," the family said a Feb. 20 posting on ING jordenrundt.info. ING is the name of their boat.
Two days later, that standoff ended with four Americans being killed by their Somali captors.
It's unclear if the Danish family knew about the deaths of the Americans. The family's last posting on Feb. 23 — a day before the hijacking — only said its journey was uneventful and "we have NOT been boarded by pirates."
The blog identified the family as Jan Quist Johansen, his wife Birgit Marie Johansen, their sons Rune and Hjalte and their daughter Naja. They are from Kalundborg, 75 miles (120 kilometers) west of Copenhagen.
The chairman of the Kalundborg yacht club, Ole Meridin Petersen, confirmed their names to The Associated Press. He called them "experienced sailors" and said they were planning to enter the Mediterranean Sea through the Suez canal from the Red Sea.
That route would take the family through the Gulf of Aden, one of the most dangerous waterways in the world in terms of piracy.
"They expected to be home in August," Meridin Petersen told the AP.
Somali pirates have extended their range east and south after increased naval patrols in the Gulf of Aden. They hold more than 660 hostages and some 30 vessels. If a ship's owner is unable to pay the multimillion dollar ransoms the pirates demand, they may keep it and use the boat to stalk other vessels until they run out of supplies or break down.
Mohamed said pirates are discussing how much ransom to demand for the Danish hostages, but pirates and investors backing this particular gang are angling for a large sum.
Reports varied as to how much a British sailing couple that was released in November after more than a year in captivity paid for their release, but it was believed to be in the region of around $1 million. Pirates are now commanding roughly $5 million for hijacked ships and crews.
In the blog, family members wrote they felt reassured as they saw overflights by counter-piracy patrol planes and had daily contact with naval authorities.
"It is reassuring that they look after us," a Feb. 20 blog post said.
A day earlier, the family blogged they had drawn up "a piracy plan for who does what if we are attacked." They were also sending daily position and status updates to the British Royal Navy's UK Maritime Trade Operations, which acts as a liaison for ships traveling through waters threatened by pirates.
The Johansens had been reporting the position of their yacht daily via e-mail since Feb. 17, said Wing Cmdr. Paddy O'Kennedy, a spokesman for the European Union's anti-piracy force.
O'Kennedy said that the EU Naval Force had written an open letter to European governments, yachting organizations and magazines warning of the dangers of sailing through the area threatened by pirates.
"You are strongly advised not to do this. It is incredibly dangerous," he said. "We did everything we possibly could to advise the yachting fraternity of the danger ... They (the family) were aware of the risks they were about to take."
The EU and other warships do not provide escorts for individual ships, although they do patrol a maritime corridor that shipping is urged to stick to. Reporting a daily position, like the Johansens did, might give a warship a slightly quicker reaction time but even that did not mean a ship under attack could be reached in time, he said.
"Even traveling in groups is not a protection for yachts. It's just a bigger target for the pirates," he said. "When you're on a yacht, it can take seconds from when (the pirates) are seen to when they're onboard."
Denmark's Foreign Ministry on Tuesday advised citizens against traveling in sailboats in the Gulf of Aden, the Arabian Sea and the northwestern Indian Ocean. Ministry officials said they confirmed the Danish boat was seized by pirates and were doing "everything in our power" to help the Danes.
Associated Press reporters Katharine Houreld and Malkhadir M. Muhumed in Nairobi, Kenya, contributed to this report.