The World Health Organization announced on Saturday an increase in the number of confirmed cases of swine flu, but said there was no evidence of sustained community spread outside of North America, which would lead to raising the pandemic alert.

“At the present time, I would still propose that a pandemic is imminent because we are seeing transmission to other countries,” Dr. Michael J. Ryan, the director of the World Health Organization global alert and response team, said in a teleconference on Saturday from Geneva. “We have to expect that Phase 6 will be reached. We have to hope that it is not.”

The organization said that 15 countries had reported a total of 615 cases of the infection, officially known as influenza A(H1N1), up from 367 cases late Friday. Dr. Ryan said that several countries in Europe reported additional confirmed cases on Saturday, including France, Germany, Spain, Great Britain, Israel, but he added: “There are a very small number of cases, it is very limited. At this stage it would be unwise to say that those events are out of control.”

In the United States, the number of confirmed cases rose to 160 in 21 states, up from 141 cases in 19 states, the Centers for Disease Control and Prevention announced on Saturday morning.