MEXICO CITY — Mexico's top health official said today the number of new swine flu cases is stabilizing in the nation at the epicenter of the outbreak.

Health secretary Jose Angel Cordova told a news conference he hoped the trend will continue and that a vaccine would be available in six months. European health ministers said they would speed efforts to develop such a vaccine.

The World Health Organization's flu chief, reacting to similar comments from other Mexican officials, cautioned that case numbers often go up and down, and said the WHO had yet to see concrete evidence that swine flu, believed to have killed 168 people in Mexico, was leveling off.

"It's a mixed pattern out there," Fukuda said. "What's happening in one part of the country is not necessarily what's happening in another part of the country."

New cases of swine flu were confirmed in the United States and Europe a day after the WHO said the virus threatened to become a global epidemic and raised its alert level to Phase 5, the second-highest stage, for the first time.

Health officials in the United States said today the number of confirmed cases had risen to 109. President Barack Obama told Americans the government was "taking the utmost precautions and preparations" to stop the virus.

The Mexican health secretary's comments followed similarly hopeful remarks from the mayor of Mexico City, who said statistics indicated "we are entering a period of stabilization."

In Luxembourg, European Union health ministers holding an emergency talks on swine flu agreed to work "without delay" with drugmakers to develop a pilot vaccine to fight the virus.

U.S. scientists are racing to develop the key vaccine ingredient, a strain of the virus engineered to trigger the immune system. But they cautioned today it would take months before enough doses could be ready for necessary testing in humans.

The Red Cross said today it is readying an army of 60 million volunteers who can be deployed around the world to help slow the virus' spread, including by educating people about hygiene and caring for the sick.