WASHINGTON — Stepping up pressure on Moscow, the U.S. on Sunday released satellite images it says show that rockets have been fired from Russia into neighboring eastern Ukraine and that heavy artillery for separatists has crossed the border.

The images, which came from the U.S. Director of National Intelligence and could not be independently verified by The Associated Press, show blast marks where rockets were launched and craters where they landed. Officials said the images show heavy weapons fired between July 21 and July 26 — after the July 17 downing of Malaysia Airlines Flight 17.

The four-page memo is part of the Obama administration’s push to hold Russia accountable for its activities in neighboring Ukraine, and the release could help to persuade the United States’ European allies to apply harsher sanctions on Russia.

The timing of the memo also could be aimed at dissuading Russia from further military posturing. The Pentagon said just days ago that the movement of Russian heavy-caliber artillery systems across its border into Ukraine was “imminent.”

Moscow has angrily denied allegations of Russia’s involvement in eastern Ukraine. Russia’s foreign ministry over the weekend accused the U.S. of conducting “an unrelenting campaign of slander against Russia, ever more relying on open lies.”

Secretary of State John Kerry spoke by phone Sunday with Russian Foreign Minister Sergei Lavrov, urging him to stop the flow of heavy weapons and rocket and artillery fire from Russia into Ukraine, said a State Department official. Kerry did not accept Lavrov’s denial that heavy weapons from Russia were contributing to the conflict, said the official, who spoke on condition of anonymity to provide details of the call.

There was no immediate comment from Moscow. The White House had no separate comment on the release, referring queries to the State Department.

The U.S. images claim to show multiple rocket launchers fired at Ukrainian forces from within Ukraine and from Russian soil. One image shows dozens of craters around a Ukrainian military unit and rockets that can travel more than seven miles.

The memo said one image provides evidence that Russian forces have “fired across the border at Ukrainian military forces and that Russian-backed separatists have used heavy artillery provided by Russia in attacks on Ukrainian forces from inside Ukraine.”

Another satellite image depicted in the memo shows “ground scarring at multiple rocket launch sites on the Russian side of the border oriented in the direction of Ukraine military units within Ukraine.”

“The wide areas of impact near the Ukrainian military units indicates fire from multiple rocket launchers,” the memo said.

Moreover, the memo included a satellite image that it called evidence of self-propelled artillery only found in Russian military units “on the Russian side of the border oriented in the direction of a Ukrainian military unit within Ukraine.”