UNITED NATIONS — UN members on Friday overwhelmingly backed negotiations on a global treaty to regulate the world’s $55 billion weapons trade, but two big arms suppliers, Russia and China, refused to support the measure.

Most top arms suppliers — the United States, Britain, France and Germany — backed a resolution in the disarmament committee of the United Nations General Assembly that will guide negotiations on a treaty.

Only Zimbabwe voted against it, and 19 countries abstained, including major arms producers Russia, China, India and Pakistan. The resolution gained 153 votes in favor.

Despite the abstentions, diplomats said most of them planned to participate in formal negotiations on the treaty, set to begin next year.

The diplomats added that the decision by Russia and China to abstain showed there was less than unanimous support for global regulations among the big arms suppliers — and indicated treaty negotiations would be tough.