WASHINGTON (AP) — The presidents of the U.S. and China agreed Friday that a planned rocket launch by North Korea would violate U.N. sanctions, the White House said, amid signs the isolated nation was moving closer to blastoff.

Commercial satellite imagery analyzed by U.S. researchers showed tanker trucks at the launch pad at the Sohae facility on North Korea's west coast. That is likely to fill fuel and oxidizer tanks, in preparation for what North Korea says is the launch of an Earth observation satellite but which the U.S. calls a ballistic missile test.

North Korea this week announced the launch would take place between Feb. 8 and 25. It would follow the government's announcement of a purported hydrogen bomb test last month that has deepened international concern over its progress toward having a nuclear bomb that can be mounted on a long-range missile.

President Barack Obama and Chinese President Xi Jinping spoke by telephone Friday and agreed that the launch would be another "provocative and destabilizing" action in violation of multiple U.N. Security Council resolutions, a White House statement said.

They reaffirmed their refusal to accept a nuclear-armed North Korea, as well as to the "complete and verifiable" denuclearization of the Korean Peninsula. The leaders also emphasized the need for a united international response to North Korea's actions, including through the U.N. Security Council, the statement said.

But the U.S. has appeared more eager than China, the North's only ally and its main source of economic support, to crank up sanctions.

Chinese state news agency Xinhua, in its dispatch about the call between the two leaders, said Xi stressed that the current situation on the peninsula is "complicated and sensitive."

A North Korean launch is considered a violation of U.N. sanctions as similar technology can be used for ballistic missiles.

The North Korea-focused website, 38 North, said in an analysis the evidence from satellite imagery taken on Wednesday and Thursday doesn't mean the North has starting filling a rocket with fuel, but is probably taking a preparatory step. It says that in the past, such activity has happened one to two weeks before blastoff.

The website said it is not yet clear if a rocket is on the launch pad.

But there's been continuing activity this week at a building at Sohae, the analysis said. In the past, the site has been used to assemble the sections of a rocket in a horizontal position and test the connections before shifting them to mount vertically at the launch pad.

It was from Sohae that North Korea blasted a rocket into space for the first time in 2012, mounted with a satellite that experts say malfunctioned soon after it entered orbit.

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Associated Press writer Darlene Superville contributed to this report.