The U.S. could seek action in the U.N. Security Council -- a move that China may not block -- if North Korea launches a rocket, a U.S. official said Wednesday.

China's President Hu Jintao did not say that his country would block Security Council action if the U.S. filed a resolution against North Korea, which has notified the international community that it will launch a rocket between April 4 and April 8. 

"The Chinese are concerned about the prospect of a launch," the American official told reporters. "They have not said that they would block action."

A report Wednesday evening by CNN cited an unnamed military source saying North Korea had begun fueling the rocket, but a senior U.S. official with knowledge of movements in the region told FOX News that, despite activity at the launch pad, there was no evidence that fueling had taken place.

Hu and President Obama met Wednesday in London ahead of the G20 summit in their first face-to-face meeting since Obama became commander in chief. The two did not mention North Korea specifically, but Obama stressed the increasingly intertwined relationship of China and the United States.

"Our economic relationships are very strong. And I've said publicly, and I continue to believe, that the relationship between China and the United States is not only important for the citizens of both our countries, but will help to set the stage for how the world deals with a whole host of challenges in the years to come," Obama said.

"Sound China-U.S. relationship is not only in the fundamental interest of our two peoples and our two countries, but also contributes to peace, stability and prosperity in the Asian Pacific region and in the world at large," Hu said.

North Korea last week warned the United Nations against taking any action for Pyongyang's launch, saying it would be considered a hostile action. North Korea claims that it is launching a satellite, but a senior administration official traveling with the president noted that the same technology used for satellites is also used for nuclear-tipped missiles.

Obama made clear in talks with world leaders, including Hu, that the U.S. "is deeply concerned about the prospective missile launch," the official said. 

The official said any launch is provocative to the region and contrary to U.N. Security Council resolutions. 

"There will be a reaction to it," the official said, noting that U.S. diplomats at the U.N. will discuss a response. The official added that the administration wants to see the six-party talks with North Korea continue. The U.S., South Korea, Japan, Russia and China have been in discussions with North Korea in an attempt to keep Pyongyang from developing nuclear weapons.

Another senior administration official said that Obama and Russian President Dmitri Medvedev both "expressed their concern about developments" in North Korea as well as Iran during an earlier meeting on Wednesday.