The US says it will not call for a UN Security Council meeting over North Korea's missile tests because it would produce "nothing of consequence".
Such a meeting would send a message to North Korea that the international community was unwilling to challenge it, US Ambassador Nikki Haley said.
Pyongyang said its tests proved that the entire US was within range.
The US has responded by testing an anti-missile system and flying bombers over the Korean peninsula.
Ms Haley said in a statement that North Korea was already subject to numerous security council resolutions that they "flout with impunity".
"An additional Security Council resolution that does not significantly increase the international pressure on North Korea is of no value," she said.
"In fact it is worse than nothing because it sends the message to the North Korean dictator that the international community is unwilling to seriously challenge him."
She urged China to rein in North Korea.
"China must decide whether it is finally willing to take this vital step. The time for talk is over," she added.
On Friday, North Korea test-fired a second intercontinental ballistic missile (ICBM).
The launch came three weeks after the state's first ICBM test.
Responding, the US military said a projectile fired by the US Air Force had been intercepted over the Pacific by a Terminal High Altitude Area Defense (Thaad) unit in Alaska.
Despite fierce objections from China, the US military has begun installing the Thaad system in South Korea with the aim of shooting down any North Korean missiles fired at the South.
US B-1 bombers conducted exercises over the Korean peninsula with South Korean and Japanese planes on Saturday.
Following the most recent test, US President Donald Trump criticised China for not doing enough to stop Pyongyang's weapons programme while making "billions of dollars" in trade with North Korea.
Mr Trump wrote on Twitter that he was "very disappointed" with China, adding that he would not allow the country to "do nothing" about the isolated state.
But Victor Gao, a former diplomat and Chinese government adviser, said that Mr Trump's comments were unhelpful, adding that the US was acting like a "spoiled child".
China, which shares a land border with North Korea and is its closest economic ally, earlier condemned the North's test launch and urged restraint on all sides.
Mr Trump and his Chinese counterpart Xi Jinping discussed North Korea during talks earlier this year, after which US officials said the two countries were working on "a range of options".
But Friday's ICBM launch demonstrates a defiance from the North, which is showcasing "a significant advancement in technology", South Korea said.