Higher rates of the preventable but contagious disease - which can kill a child or leave it blind, deaf or brain-damaged - have been recorded in all regions, the United Nations agency said in a statement, appealing for better vaccination coverage.
Fresh outbreaks have hit the Democratic Republic of the Congo, Ethiopia, Georgia, Kazakhstan, Kyrgyzstan, Madagascar, Myanmar, the Philippines, Sudan, Thailand and Ukraine, "causing many deaths - mostly among young children," the WHO said, Presstv Reported.
It gave no figures for fatalities but noted it estimates that only one in 10 cases is reported globally.
"Over recent months, spikes in case numbers have also occurred in countries with high overall vaccination coverage, including the United States of America as well as Israel, Thailand, and Tunisia, as the disease has spread fast among clusters of unvaccinated people," the WHO statement said.
US federal health officials said on Monday the number of confirmed cases of measles in the United States this year jumped by nearly 20 percent in the week ended April 11 - the country's second-worst outbreak in nearly two decades.
A growing and vocal fringe of parents in the United States oppose measles vaccines in the belief, contrary to scientific evidence, that ingredients in the vaccines can cause autism or other disorders.
Increasing vaccination coverage maximizes a population's protection, WHO said.
Global coverage with the first dose has "stalled" at 85 percent, against 95 percent needed to prevent outbreaks, while 25 countries still do not include a second dose in their national programs, it said.