Singapore ? The sinking of a South Korean warship is part of a reckless pattern of aggression by North Korea, U.S. Defense Secretary Robert Gates said Saturday, as the U.S. and its allies turned up the rhetorical heat on the communist country.

“This sinking is far more than a single, isolated incident,” Gates told Asian defense officials at a conference in Singapore. Answering questions from delegates later, Gates said there must be consequences for what he called an unprovoked assault.

“For nothing to happen would be a very bad precedent,” he said.