By the time the Nivose crew boarded the whaler, all that remained were fuel barrels, which were insufficient evidence to try the three men for piracy.

The Nivose crew left the seafarers with enough fuel, food and water to retreat to the shores of Somalia, the world's incubator of modern-day pirates.

The confrontation illustrates the general failure of stepped-up security measures to curb piracy off the Horn of Africa.

The European Union Naval Forces launched patrols to combat piracy in the Somali Basin in 2008. Thirty nations and international groups partnered in a Contact Group with the same goal in 2009.

Since then, the number of pirate hijackings has increased to 47 from 46, while the average ransom paid to release hostages jumped from $3.4 million in 2009 to $5.4 million last year, according to the nonprofit One Earth Future Foundation.

Where authorities have grown more aggressive — such as in the Gulf of Aden, where 33,000 vessels transit each year and 50 last year were hijacked — Somali pirates have become more sophisticated. Their operations have evolved into well-defined hierarchies including planners, financiers and seafarers who use mother ships to launch and resupply smaller, high-speed skiffs.

Stronger naval presence, including the multinational task forces that patrol the waters with some 20 ships at any given time, has led pirates to expand their geographical scope — north toward the Straits of Hormuz, south toward Mozambique and east nearly to India.

As of last week, pirates were holding 25 vessels and 577 hostages, according to the European Union Naval Forces.

Cost of piracy

The pirates also have turned more ruthless, using captives as human shields and broadening their targets to include recreational boats.

At least three pleasure boats have been attacked since last month, including one with four Americans whom the pirates killed when Navy SEALs attempted to free them.

A Danish family with three children remain in pirate custody after a rescue attempt by authorities in the semi-autonomous region of Puntland in northeastern Somalia failed on March 10, leaving five soldiers dead.

The United States "is concerned about [media] reports of increasingly abusive treatment of captive mariners by pirates, there is insufficient information at present to determine if such a dramatic shift in piracy tactics has truly occurred," a State Department spokesman told The Washington Times.

However, there is little doubt about the huge toll piracy is taking on commerce and stability in the region.

Piracy cost the international community $7 billion to $12 billion last year, according to estimates from the One Earth Future Foundation. The price tag is expected to rise, with 13 pirate raids already recorded off the Horn of Africa since January — a pace set to outstrip last year's total.

Most of that estimate is attributable to the cost of rerouting ships.

The alternative of arming and insuring commercial ships could be even more costly because many vessels passing the Horn of Africa are low-value cargo carriers with tight profit margins. Fewer than 10 percent of vessels passing through the Gulf of Aden are insured, and insurance premiums are rising.

"Most can't afford the expense of armed security personnel, and some of the low-cost carriers do not buy insurance," said David Shinn, adjunct professor of international affairs at George Washington University and former U.S. ambassador to Ethiopia and to Burkina Faso.

"They have made the decision that they will take their chances with getting captured, which in any given year accounts for less than one-tenth of 1 percent of the sailings in the region. It is an economic decision."

Kenya Shippers Council estimates that piracy increases the cost of imports by $23.8 million per month and exports by $9.8 million, with costs passed on to consumers, pushing up prices of imported goods by 10 percent, said Andrew Mwangura, maritime editor of Somalia Report.

Piracy's threat to fishing and tourism has shaved $10.5 billion off the Seychelles' economy, about 4 percent of the island nation's gross domestic product, he said.

Now, with ransom sums rising, there is mounting concern in Washington about where the money might end up.

Pirates and terrorists

The departments of Defense, Justice, State and Treasury all collect data on pirate financing, but none has taken the lead to build cases against pirate leaders and financiers, some of whom could have ties to terrorist groups.

Rep. Frank A. LoBiondo, a New Jersey Republican who recently chaired a subcommittee hearing on piracy, expressed concern that not enough is being done to track ransom payments.

"I am extremely concerned piracy could be benefiting the terrorist groups operating in Somalia and that these groups could use their profits to carry out terrorist acts here at home and abroad," Mr. LoBiondo said.

Some observers fear that terrorist groups, such as the Somali-based al-Shabab, could be cooperating with the pirates, who offer terrorists lessons in seamanship in exchange for weapons.

More Yemenis are being linked to piracy: One was indicted March 10 by a Virginia grand jury in connection with the four Americans killed aboard a yacht last month. Yemen is also a haven for al Qaeda terrorists.

Other observers find scant evidence of a direct connection between pirates and terrorist groups.

They say the pirates are well-armed from an abundance of weapons left over from Somalia's long civil war and trickling in from Yemen. The pirates also get financial and logistical support from mafia-style Somali businessmen in East Africa and other areas, they say.

Pacts with terrorists could be forged, however, if anti-piracy efforts start netting better results.

"The nagging question I have is what would the pirates do if they were pressed any further, for example, by more robust counteraction translating into dead pirates, or a general refusal of all states involved to pay ransom," said Peter Lehr of the Center for the Study of Terrorism and Political Violence at Scotland's University of St. Andrews.

The United States has taken the lead in prosecuting pirates, although no Somali pirate has ever successfully taken control of a U.S. commercial vessel. Last month, the only surviving pirate who attacked the Maersk Alabama merchant ship off Somalia's coast in April 2009 was sentenced to 33 years in prison.

The 13 Somali pirates and one Yemeni accused of boarding a yacht that led to the four American deaths were indicted by a grand jury this month. If convicted, they will face a mandatory life sentence.

Last week, a Virginia court imposed life sentences to five pirates who tried to hijack a U.S. naval ship last year. The sentences were handed down days before pirates killed Somali authorities trying to rescue a captive Danish family. They threatened to kill the family if any further rescue attempts were made.

A stronger naval presence might help to some degree, said William Wechsler, deputy assistant secretary of defense for counternarcotics and global threats.

"In order to have 100 percent coverage of 2.5 million square nautical miles, it would require more ships than are currently in the inventory of the world's navies," he said.

Some specialists advocate sinking pirate-held ships after ensuring that no hostages are on board.

More authorities are calling for ships to arm themselves and take other countermeasures such as cruising with escorts. Many shippers leave themselves dangerously unequipped because they naively assume that militaries will come to their rescue.

"We note that in all cases where armed private security teams have been used, they have successfully kept pirates from boarding their vessel," said Mr. Wechsler.