North Korea said Wednesday it would halt reunions of relatives split by the heavily fortified border, and South Korea's president made his strongest comments yet against the communist nation's recent missile tests in a further blow to reconciliation efforts.

In the wake of a U.N. Security Council resolution against the North's launches, Japanese Prime Minister Junichiro Koizumi said Tokyo won't rush to impose more sanctions on Pyongyang while it waits for a response from the reclusive country.

On July 5, the North defied international opposition and tested a long-range missile believed capable of reaching the U.S., along with six other short- and medium-range missiles. The move prompted the Security Council to pass a resolution over the weekend barring U.N. member countries from missile-related dealings with the North.

The missile crisis has become one of the strongest challenges yet to South Korea's policy of engagement with the North.

The North-South family reunions had been a key element of reconciliation efforts since the first and only summit between leaders of the North and South in 2000, bringing together more than 16,300 Koreans for tear-filled meetings of several days.

Many of those wishing to take part in the reunions are elderly, hoping before they die for a glimpse of relatives unseen since the 1953 cease-fire that halted the Korean War.

The North said Wednesday it wouldn't allow the reunions to go on because the South refused to discuss humanitarian aid at high-level talks last week between the two Koreas. South Korea had sought to address the North's missile and nuclear programs, but the North brushed off the plea saying the issues were irrelevant to that forum.

"The humanitarian undertakings have virtually ceased to exist between the North and the South as your side has abused even the humanitarian issue for meeting its sinister purpose to serve the outsiders," Jang Jae On, head of the North Korean Red Cross Society, wrote in a letter to his South Korean counterpart.

"Our side is, therefore, of the view that it has become impossible to hold any discussion related to humanitarian issues, to say nothing of arranging any reunion between separated families," Jang wrote, according to the North's official Korean Central News Agency.

Also Wednesday, South Korean President Roh Moo-hyun condemned North Korea for potentially sparking an arms race with the missile tests, but also cautioned other countries that provocative responses could raise regional tension.

"North Korea's missile launches are wrong behaviors that not only violate peace and stability on the Korean Peninsula and increase tension, but spark an arms race that doesn't help anyone," Roh told a meeting of top security officials, according to presidential adviser Song Min-soon.

However, Roh said, "behaviors that create unnecessary tensions by responding excessively ... don't help solve the issue."

He didn't name any country, but has previously criticized Japan for reportedly considering a pre-emptive strike against North Korea's missile test site.

Koizumi said Tokyo was taking a cautious approach to its own sanctions against the North after the U.N. resolution and a Group of Eight summit statement against the missile launches.

"North Korea should take the resolution and the (G-8) chairman's statement seriously. I think it's better for us to wait and see," the Japanese leader told reporters.

Calls were also growing for the North to return to six-country talks on its nuclear program, which it has refused to attend since November in anger over U.S. financial restrictions for Pyongyang's alleged illegal financial activity.

South Korean officials said Wednesday that discussions were under way for the five other countries at the talks — China, Japan, Russia, South Korea and the United States — to meet without the North Koreans.

South Korean presidential adviser Song stressed that five-way talks, if held, "won't be talks to put pressure on one party," but would be "part of a process to make constructive and real progress at the six-party talks."

In another blow to North-South relations, the two Koreas appeared likely to delay this week's talks on forming a unified team for the 2008 Beijing Olympics, the South's Korea Olympic Committee said Wednesday.