US secretary of state Hillary Clinton said the US government would try to seize the financial assets and property of pirates while working with shippers to thwart hijackers off the coast of Somalia.
The measures outlined by Mrs Clinton, part of a new US diplomatic initiative to tackle sea piracy, are largely stopgap and symbolic moves while officials consider more comprehensive diplomatic and military action.
The exploratory effort to track and freeze pirate assets will be difficult to implement because of the highly localised and informal nature of their economy, which seldom uses regulated areas of the international financial system, current and former officials said.
As part of the package, Mrs Clinton said the administration would also call for immediate meetings of an international counter-piracy task force to expand naval co-ordination against pirates.
She said agencies would meet tomorrow to review the problem and consider its responses before an international conference on Somali piracy and development next week.
She also warned that the US "does not make concessions or ransom payments to pirates".
Mrs Clinton acknowledged that the diplomatic steps she outlined would not necessarily deal with piracy's root causes, which are endemic instability and insecurity on the ground in Somalia.
But she said the moves were still critical given the rising number of ship hijackings, including last week's attack on a US-flagged ship that ended with an American hostage freed and three pirates killed by navy snipers.
"You've got to put out the fire before you can rebuild the house," she said at the US State Department. "And right now we have a fire raging."
Mrs Clinton talked of "going after" pirate bases on the ground in Somalia, a "hot pursuit" policy that was authorised by the United Nations in December but has not yet been undertaken by the US because of liability concerns among military officials.
"These pirates are criminals, they are armed gangs on the sea. And those plotting attacks must be stopped," she said.
"We may be dealing with a 17th-century crime, but we need to bring 21st-century solutions to bear."
Mrs Clinton said she wanted the United States and others to "explore ways to track and freeze" pirate ransom money and other funds used in buying new boats, weapons and communications equipment.
"We have noticed that the pirates are buying more and more sophisticated equipment, they're buying faster and more capable vessels, they are clearly using their ransom money for their benefit - both personally and on behalf of their piracy," she said.
"We think we can begin to try and track and prevent that from happening."
However, a former Bush administration official who worked on piracy and on steps to stop the financing of terrorist groups at the National Security Council and US Treasury said such action would be "extremely difficult".
"These are local networks that aren't necessarily putting their cash into bank accounts or attempting to transfer it out of the area," said Juan Zarate.
"Their assets rarely touch either the formal or informal global financial system."