The World Health Organization said Thursday that a new flu strain continued to spread, particularly in Mexico and the U.S., but refrained from declaring a global pandemic even as more countries confirmed cases. Amid a growing debate around the globe about travel restrictions, the United Nations public-health agency raised the number of confirmed cases of the A/H1N1 virus to 236 from the 148 reported Wednesday. The biggest jump was in Mexico, where the number of confirmed cases rose to 97 from 26. Meanwhile, the Centers for Disease Control and Prevention said the number of confirmed cases in the U.S. rose to 109 in 11 states, up from 91 in 10 states the day before. "This is a rapidly evolving situation. It's a situation filled with uncertainty," Richard Besser, the CDC's acting director, told reporters. Still, Keiji Fukuda, the WHO'S top flu official, said in a separate news conference that there was no reason at this time to raise its global pandemic alert to phase 6