The United Nations Security Council moved closer on Tuesday to expanding sanctions on North Korea for its nuclear and ballistic missile activities. The United States and China introduced a resolution that would target North Korean bankers and overseas cash couriers, tighten inspections of suspect ship and air cargo, and subject the country’s diplomats to invasive scrutiny and increased risk of expulsion.

Passage of the measure, drafted in response to the third North Korean underground nuclear test three weeks ago, seemed all but assured, in part because China — North Korea’s major benefactor — participated in drafting the language. It would be the fourth Security Council sanctions resolution on North Korea, which has defied the previous measures with increasing belligerence. A vote was expected on Thursday.

Infuriated, North Korea vowed to scrap the 1953 armistice that halted the Korean War and threatened to attack the United States with what the North Korean government news agency called an arsenal of diverse “lighter and smaller nukes.”

American officials played down the North Korean warning, which echoed bombastic admonitions that have become part of the standard fare from the North. Still, the threat of a North Korean nuclear attack seemed all the more provocative, coming two days after North Korea conveyed a message of friendship to a visiting American group that included Dennis Rodman, the former basketball star.