Russian President Vladimir Putin on Friday signed into law legislation completing the annexation of Crimea, calling it a "remarkable event."
The Kremlin signing ceremony took place after the Federation Council, the upper house of Russia's parliament, voted unanimously to incorporate the Crimea region into Russia. The lower house ratified the treaty on Thursday, just four days after Crimean residents voted in a referendum to break away from Ukraine and join Russia.
President Putin and Crimean leaders signed the treaty on Tuesday, and the Kremlin said the treaty came into force on the date it was signed.
In a meeting Friday with his advisory Security Council, Mr Putin said for now, Russia will hold off on imposing sanctions on the United States in retaliation for U.S. sanctions against Russia over the Ukraine crisis.
However, his spokesman, Dmitry Peskov, told reporters separately that Russia will respond in kind to the latest U.S. sanctions, which target Russian officials and members of President Putin's inner circle. "We will respond every time," Peskov said.
And the Russian Foreign Ministry said in a statement Friday that Russia will "respond harshly" to the latest round of U.S. sanctions.
U.N. Secretary-General Ban Ki-moon is meeting Friday with Ukraine's acting president, Oleksandr Turchynov, and acting Prime Minister Arseniy Yatsenyuk in Kyiv for discussions on resolving the crisis. On Thursday, Mr. Ban met with President Putin and Russian Foreign Minister Sergei Lavrov in Moscow. Mr. Ban said he urged the Russian leader to prevent "any unintended incident" in or near Ukraine that could aggravate tensions in the volatile region.
On Thursday, U.S. President Barack Obama announced further sanctions against Russia. Speaking at the White House, Mr. Obama said he is penalizing more individuals and a bank involved in Russia's occupation of the Black Sea peninsula. Earlier, the United States limited travel and the economic activity of several key Russians involved in the Crimea takeover.
The president also said he is considering more penalties to entire sectors of the Russian economy, as well as specific individuals. He said those plans are being formulated in conjunction with European allies.
In Brussels, meanwhile, European Union leaders added 12 people -- all Russian or Crimean -- to a list of those subject to travel bans and asset freezes. The new names were not immediately released, but the move raises the number of people subject to EU sanctions to 33.
Moscow retaliated against the U.S. sanctions with travel bans on nine Americans, including Republican Senator John McCain, Democratic Senate Majority Leader Harry Reid and Republican Speaker of the House of Representatives John Boehner.
In another development, U.S. Defense Secretary Chuck Hagel spoke for nearly an hour with Russian Defense Minister Sergei Shoigu. A Pentagon spokesman says Hagel asked why Russian troops are deploying along Ukraine's eastern southern borders. The spokesman said Hagel was assured that the troops are conducting maneuvers and have no plans to enter Ukraine.
Ukrainian officials say armed pro-Russian forces seized three Ukrainian warships in Crimea's Sevastopol Bay Thursday.
Ukraine authorities said Tuesday that Kyiv has drawn up plans to evacuate Crimea, and will seek U.N. support in turning the peninsula into a demilitarized zone. Ukraine Defense Council Secretary Andriy Parubiy also said Ukraine is planning to hold military maneuvers "with our allies." He did not elaborate.