The killing of three Somali pirates in the dramatic U.S. Navy rescue of a cargo ship captain has sparked concern for other hostages and fears that the stakes have been raised for future hijackings in the busy Indian Ocean shipping lane.

Sunday's rescue of Capt. Richard Phillips from his captors aboard a drifting lifeboat followed a shootout at sea on Friday by French navy commandos, who stormed a pirate-held sailboat, killed two pirates and freed four French hostages. The French owner of the vessel was also killed in the assault.

The two operations may have been a setback for the pirates but they are unlikely to quell the brigands, who have vowed to avenge the deaths of their comrades.

Experts indicated that piracy in the Indian Ocean off Somalia, which transformed one of the world's busiest shipping lanes into one of its most dangerous, has entered a new phase with the Navy SEAL rescue operation of Phillips.

It "could escalate violence in this part of the world, no question about it," said Vice Adm. Bill Gortney, commander of U.S. Naval Forces Central Command.

The International Maritime Bureau said Monday it supported the action by the U.S. and French navies, but cautioned it may spark retaliatory moves by pirates.

"We applaud the U.S. and the French action. We feel that they are making the right move, although the results sometimes may be detrimental," said Noel Choong of the IMB's piracy center in Kuala Lumpur.

He did not elaborate, but for families of the 228 foreign nationals aboard 13 ships still held by pirates, the fear is revenge on their loved ones.

"Those released are lucky, but what about those who remain captive?" said Vilma de Guzman, the wife of Filipino seafarer Ruel de Guzman. He has been held by pirates since Nov. 10 along with the 22 other Filipino crew of the chemical tanker MT Stolt Strength.

The U.S. rescue operation "might be dangerous (for) the remaining hostages because the pirates might vent their anger on them," she said.

So far, Somali pirates have never harmed captive foreign crews except for a Taiwanese crew member who was killed under unclear circumstances. In fact, many former hostages say they were treated well and given sumptuous food.

The pirates had operated with near-impunity in the Gulf of Aden north of Somalia, and more recently in waters south of the country after a multinational naval force began patrolling the Gulf.

Choong said there have been 74 attacks this year with 15 hijackings as compared to 111 attacks for all of last year.

The modus operandi of the pirates is simple: Board unarmed or lightly armed merchant ships, fire shots in the air or at the hull to intimidate the crew, divert the ships to hide-outs on the Somali coast and wait for the owners to pay millions of dollars in ransom.

But the game changed last week when the pirates boarded the U.S.-flagged Maersk Alabama. In an act of courage, Phillips offered himself as hostage in return for the safety of his crew.

The pirates transferred the 53-year-old Phillips, a Vermont native, to a lifeboat. But the pirates had not counted on the U.S. military's resolve. After a five-day standoff during which a small U.S. flotilla tailed the lifeboat, Navy Seal snipers on a destroyer shot and killed three pirates and plucked an unharmed Phillips to safety. A fourth surrendered.

The comrades of the slain pirates immediately threatened retaliation.

"From now on, if we capture foreign ships and their respective countries try to attack us, we will kill them," said Jamac Habeb, a 30-year-old self-proclaimed pirate, told The Associated Press by telephone from the pirate hub, Eyl.

Abdullahi Lami, one of the pirates holding a Greek ship in the pirate den of Gaan, a central Somali town, told the AP that pirates will not take the U.S. action lying down.

"We will retaliate for the killings of our men," he said.

Giles Noakes, chief maritime security officer of the largest international shipping association, the Denmark-based BIMCO, says it is premature to say Philips' rescue will lead to an escalation of violence.

"The question here is whether there will be a change of attitude in the pirates and in their modus operandi. We hope the change will be that they will be even more deterred because of the successful action by both the Maersk Alabama crew and the navies," he said.

Many of the governments whose ships have been captured — including Taiwan's Win Far 161 with a multinational crew of 30 — are in talks with the pirates and would not comment on the consequences of the American rescue for fear of jeopardizing the negotiations.

"We are monitoring the situation closely, but the ship owner wants to keep a low profile to help with their negotiation with the abductors," Taiwanese Foreign Ministry spokesman Henry Chen said.

He said the crew, comprising 17 Filipinos, six Indonesians, five Chinese and two Taiwanese, were safe as of Monday.

Some families also wonder if Phillips' rescue drew so much of attention because of his nationality.

"It's difficult when the ship's crew are all Filipinos because we are ignored," said de Guzman. "Maybe if there are Japanese, Koreans or British among the crew, the case would get more attention."