Officials from Japan and South Korea met in Seoul on Friday and agreed to call on China to exert influence over Pyongyang to prevent the launch.
China is one of Pyongyang's very few influential supporters, but Beijing has also expressed frustration at being unable to make the new regime of Kim Jong-un see the potential downside of any show of force.
Instead, China has called on all sides from taking action that "would complicate the situation on the Korean peninsula."
Gary Samore, a key defence adviser to President Barack Obama, said in Seoul on Friday that North Korea faces a "strong response" if it does not heed the wishes of the international community and goes ahead with the launch.
"I really can't speculate on why they are doing it, but we think it's a big mistake and we are trying to persuade them [against going ahead]," he said.