The new rules will have the force of international law, but don't specify penalties for noncompliance. WHO officials said the regulations will give them much greater authority in demanding that countries be open about disease developments.

The new regulations, which were adopted by the annual meeting of the U.N. health agency's key decision-making body, will set out the "universally accepted rules of the game," said Guenael Rodier, WHO's head of communicable diseases surveillance and response.

"This is a major step forward for international health," said WHO chief Dr. Lee Jong-wook. "These new regulations recognize that diseases do not respect national boundaries. They are urgently needed to help limit the threats to public health."

The regulations establish formal procedures for much of the activities that WHO has undertaken during recent global health threats.

A central aspect is the establishment of a pool of external public health experts who would form a committee during a global health emergency and advise the WHO on key actions, such as whether to recommend to the rest of the world that travel and commerce to and from affected areas be restricted.

Previously, such decisions were made internally by the WHO, with informal input from outside experts.

The new regulations also formalize the requirement for countries to be open about the emergence and extent of outbreaks. They do not give the WHO the authority to come in and investigate against the wishes of the affected country, but make it easier for the health agency to share the information with the rest of the world, increasing pressure on the affected nation to cooperate.

"WHO now has more power to demand information," said Rodier. "And countries realize that even if they don't tell us we will find out anyway."

All countries will be automatically bound by the rules when they take effect two years from now, unless they express reservations or opt out of the system.

The United States, which welcomed the new rules, was the first country to announce its plans to file a reservation -- saying that when it came to U.S. armed forces, it would comply with the rules unless they compromise national security.

To comply, countries must ensure they have the capacity to detect and respond to outbreaks quickly.

"We hope to get a more secure world," Rodier said.

The new rules will have the force of international law, but don't specify penalties for noncompliance. WHO officials said the regulations will give them much greater authority in demanding that countries be open about disease developments.

The rules also leave governments free to impose travel or trade sanctions against a country with an outbreak as long as the measures are justified on a scientific basis. WHO may ask for the cessation of such measures if they are scientifically unjustified.

The regulations have been on the drafting table since 2003, after the outbreak of new and more infectious diseases, such as SARS, Ebola and bird flu, made the international community more wary of worldwide pandemics.

It is the first time that the regulations include public health threats resulting from bioterrorism, chemicals spills or Chernobyl-type nuclear accidents. But several countries, including Iran and other unspecified Middle Eastern nations, opposed including such measures until very late in the negotiating process, health officials said.

The rules also oblige countries to notify the WHO of a broader list of diseases with the potential to become a global health threat.

Under the previous International Health Regulations -- which date to 1969 -- nations were required to notify the agency of any cases of yellow fever, plague and cholera. Now they will be required to disclose cases of SARS or smallpox, outbreaks of influenza caused by a strain that the population has no immunity to and cases of polio in countries considered free of the disease.

The regulations will significantly strengthen WHO's ability to combat outbreaks, Rodier said. For example, the health agency will be able to act on information from non-governmental sources, rather than only on countries themselves.

This should help WHO respond to serious health problems when governments are reluctant to share their information -- as was the case at the beginning of the SARS outbreak in China.