SEOUL, SOUTH KOREA - The United States is proposing more international sanctions against North Korea, as part of a wider effort to ramp up pressure on Pyongyang following its most recent missile tests.

The United States Wednesday strengthened its own sanctions against North Korea, designating five North Koreans it alleges are responsible for securing goods for Pyongyang's weapons programs.

On top of those measures, the United States wants the United Nations Security Council to impose stronger sanctions, according to a tweet from Linda Thomas-Greenfield, the U.S. ambassador to the United Nations.

She did not offer any more details.

There was no immediate reaction from China and Russia, which are permanent members of the Security Council and would need to approve any sanctions. Both have recently called for North Korea sanctions to be relaxed rather than strengthened.

North Korea is already barred from a wide range of economic activity under a series of Security Council resolutions. China and Russia agreed to many of those sanctions following North Korea's 2017 nuclear and long-range missile tests.

Since then, North Korea has refrained from nuclear tests or intercontinental ballistic missile launches. In 2019, though, the North resumed launches of shorter-range weapons. It has since unveiled several new systems, including many designed to evade the missile defenses of the U.S. and its allies.

Already this year North Korea has conducted two tests of what it described as hypersonic missiles. The missiles feature maneuverable reentry vehicles that detach in flight and are theoretically harder to intercept.

U.S. officials condemned the launches, pointing out that North Korea is banned from ballistic missile activity by existing U.N. sanctions.

On Wednesday, the United States went a step further. The Treasury Department sanctioned four China-based North Koreans and a Russia-based North Korean, accusing them of procuring materials for North Korea's weapons programs.

Secretary of State Antony Blinken said the United States "will use every appropriate tool" to address North Korea's weapons of mass destruction and ballistic missile programs, "which constitute a serious threat to international peace and security and undermine the global nonproliferation regime."

Taken together, the moves suggest the United States is taking a firmer stance on North Korean missile tests. Since 2019, the United States has played down North Korea's short-range launches, presumably to preserve the possibility for future talks.

State Department spokesperson Ned Price said Wednesday that the U.S. approach toward North Korea "remains unchanged."

South Korean army soldiers ride K-9 self-propelled howitzers in Paju, South Korea, near the border with North Korea, Jan. 11, 2022.

"I would strenuously object to the idea that these sanctions indicate anything other than a genuine effort to constrain North Korea's - in this case, their ballistic missile programs," Price said at a regular press briefing. The United States remains "willing, ready, and able" to engage in diplomacy with North Korea, he added.

North Korea walked away from nuclear talks in 2019 and has said it will not rejoin them until the United States drops its "hostile policy."

The United States appears to be balancing the need to respond to North Korea's tests against its goal of keeping the door open to negotiations, Eric Brewer, a former White House National Security Council official, said.

"It seems they are framing this in strictly counterproliferation terms and avoiding some of the language that would suggest a larger pressure-centric effort is in the offing," said Brewer, who now focuses on nuclear policy at the Washington-based Center for Strategic and International Studies.

Despite the apparent inability of existing sanctions to prevent North Korea from developing its nuclear weapons program, U.S. officials have defended the approach, saying it is important to set a precedent for other nations considering acquiring nuclear weapons.

"We continue to enact measures that put constraints on these WMD and ballistic missile programs, that hold proliferators and other bad actors accountable for their activity," Price said Wednesday. "We'll continue to do that."