The White House says the situation in Ukraine will be "front and center" during President Barack Obama's trip to Europe next week.
National Security Advisor Susan Rice told reporters Friday that the common theme to the president's trip is the fundamental strength of U.S. partnerships and alliances, including NATO, the European Union and the G7.
Rice said Ukraine and the Russian takeover of Crimea are prompting a fundamental reassessment of U.S.-Russian relations. She said the world will clearly see that Russia is more and more isolated.
Deputy National Security Advisor Ben Rhodes said a G-7 summit in The Hague -- a meeting that probably would have included Russia as an eighth member -- has been added to the president's agenda as part of that isolation.
Also on President Obama's European schedule is a nuclear security summit with more than 50 other countries, including Russia.
Rice says the United States has every interest in continuing to cooperate with Russia on this issue, which she calls a pillar of the Obama national security policy -- making it harder for terrorists to get their hands on nuclear materials.
Meanwhile, Russia and the rest of the OSCE agreed Friday to deploy civilian monitors to Ukraine, but there is no mention if they will go to Crimea.
The OSCE, which works by consensus, says up to 500 monitors will gather information on the security situation in Ukraine, including human rights.
The United States says the OSCE has a mandate to work in all of Ukraine, including Crimea. But Russia's ambassador to the OSCE, Andrey Kelin, said Crimea is part of Russia and the mission has no mandate there.
Russian President Vladimir Putin signed a law Friday completing the annexation of Crimea. The law recognizes parliament's approval of this week's referendum by Crimeans on breaking away from Ukraine.
The U.S. says no one in the international community will recognize Crimea as part of Russia.