TOKYO (AP) – Japan said Monday it was considering whether a pre-emptive strike on North Korea’s missile bases would violate its constitution, signaling a hardening stance ahead of a possible U.N. Security Council vote on Tokyo’s proposal for sanctions against the regime.

The vote itself could be delayed for several days, a news agency reported.

China asked Japan to postpone the vote until later this week and Japan is prepared to accept, Kyodo News agency said.

Japanese officials had earlier vowed to push ahead with a resolution that would impose sanctions on North Korea for its missile tests last week, but said Tokyo would not insist on a Monday vote.

Japanese Prime Minister Junichiro Koizumi told reporters his government wants a vote on the measure “as soon as possible.”

“I think we must send a message that’s as clear as possible” to North Korea, he said.

Japan was badly rattled by North Korea’s missile tests last week and several government officials openly discussed whether the country ought to take steps to better defend itself, including setting up the legal framework to allow Tokyo to launch a pre-emptive strike against Northern missile sites.

“If we accept that there is no other option to prevent an attack … there is the view that attacking the launch base of the guided missiles is within the constitutional right of self-defense. We need to deepen discussion,” Chief Cabinet Secretary Shinzo Abe said.

Japan’s constitution bars the use of military force in settling international disputes and prohibits Japan from maintaining a military for warfare. Tokyo has interpreted that to mean it can have armed troops to protect itself, allowing the existence of its 240,000-strong Self-Defense Forces.

A Defense Agency spokeswoman, however, said Japan has no offensive weapons such as ballistic missiles that could reach North Korea. Its forces only have ground-to-air missiles and ground-to-vessel missiles, she said on condition of anonymity because of official policy.

Japanese fighter jets and pilots are not capable of carrying out such an attack, a military analyst said.

“Japan’s air force is top class in defending the nation’s airspace, but attacking another country is almost impossible,” said analyst Kazuhisa Ogawa.

“Even if Japan’s planes made it to North Korea, they wouldn’t make it back … it would be an act of suicide,” he said. “Japan has no capacity to wage war.”

Despite resistance from China and Russia, Japan has pushed for the U.N. Security Council resolution, which would bar nations from buying or otherwise receiving missile-related items, materials goods and technology from North Korea.

“It’s important for the international community to express a strong will in response to the North Korean missile launches,” Abe said. “This resolution is an effective way of expressing that.”

China and Russia, both nations with veto power on the council, have voiced opposition to the measure. Kyodo reported Monday, citing unidentified Chinese diplomatic sources, that China may use its veto on the Security Council to block the resolution.

The United States, Britain and France have expressed support for the proposal, while Japanese Foreign Minister Taro Aso has said there is a possibility that Russia will abstain.

South Korea, not a council member, has not publicly taken a position on the resolution, but on Sunday Seoul rebuked Japan for its outspoken criticism of the tests.

“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 contributing to tensions on the Korean Peninsula.

Abe said Monday it was “regrettable” that South Korea had accused Japan of overreacting.

“There is no mistake that the missile launch … is a threat to Japan and the region. It is only natural for Japan to take measures of risk management against such a threat,” Abe said.

Meanwhile, a Chinese delegation including the country’s top nuclear envoy _ Vice Foreign Minister Wu Dawei _ arrived Monday in North Korea, officially to attend celebrations marking the 45th anniversary of a friendship treaty between the North and China.

The U.S. is urging Beijing to push its communist ally back into six-party nuclear disarmament talks, but the Chinese government has not said whether Wu would bring up the negotiations. A ministry spokeswoman said last week that China was “making assiduous efforts” in pushing for the talks to resume.

Talks have been deadlocked since November because of a boycott by Pyongyang in protest of a crackdown by Washington on the regime’s alleged money-laundering and other financial crimes.

Beijing has suggested an informal gathering of the six nations, which could allow the North to technically stand by its boycott, but at the same time meet with the other five parties _ South Korea, China, the U.S., Japan and Russia. The U.S. has backed the idea and said Washington could meet with the North on the sidelines of such a meeting.

Still, U.S. Assistant Secretary of State Christopher Hill questioned just how influential Beijing was with the enigmatic regime.

“I must say the issue of China’s influence on DPRK is one that concerns us,” Hill told reporters in Tokyo. “China said to the DPRK, ‘Don’t fire those missiles,’ but the DPRK fired them. So I think everybody, especially the Chinese, are a little bit worried about it.”

The DPRK refers to the North’s official name, the Democratic People’s Republic of Korea.

Hill is touring the region to coordinate strategy on North Korea. He has emphasized the need for countries involved to present a united front.

“We want to make it very clear that we all speak in one voice on this provocative action by the North Koreans to launch missiles in all shapes and sizes,” Hill said. “We want to make it clear to North Korea that what it did was really unacceptable.”