Tokyo ? A top U.S. envoy pushed for a united international front against North Korea’s recent missile tests Sunday, but divisions widened over a U.S.-backed Japanese proposal for sanctions against Pyongyang.

U.S. Assistant Secretary of State Christopher Hill was in Tokyo ahead of a possible vote in the U.N. Security Council on the resolution. Despite resistance from China and Russia, Japanese Foreign Minister Taro Aso vowed Sunday not to compromise on the measure’s tough wording.

South Korea has not publicly taken a position on the resolution but on Sunday issued a harsh rebuke of Japan’s outspoken criticism of the North Korean missile launches last week. “There is no reason to fuss over this from the break of dawn like Japan, but every reason to do the opposite,” a statement from President Roh Moo-hyun’s office said, suggesting that Tokyo was helping to heighten tensions on the Korean Peninsula.

North Korea also issued fresh threats. The North’s state-run Korean Central Broadcasting Station, monitored by South Korea’s Yonhap news agency, cited a previous statement by leader Kim Jong Il vowing “to answer to an enemy’s retaliation with retaliation and to an all-out war with an all-out war.”

China and Russia, two of North Korea’s traditional allies, remained the two veto-wielding permanent members of the Security Council who have voiced opposition to the resolution, which Japan hopes to put to a vote today.

Despite the divisions, a top U.S. diplomat voiced optimism about forming a common strategy and urged China to put pressure on North Korea to end its launches and to return to international nuclear disarmament talks.

Undersecretary of State Nicholas Burns, on CNN’s Late Edition, said Sunday the United States hopes Beijing will “exert some pressure on the North Korean regime to get it to come back to the six-party talks and end these missile tests.”

Hill, who arrived in Japan after stops in Beijing and Seoul, denied any deep split over North Korea or the Japanese resolution.

“I don’t see any splintering. On the contrary, I see a very clear message,” Hill said in Tokyo.