The United States and Russia failed on Friday to resolve a Cold-War-style crisis sparked by Moscow's military intervention in Crimea and the Ukrainian peninsula's weekend referendum on joining Kremlin rule.

U.S. Secretary of State John Kerry met his Russian counterpart Sergei Lavrov in London with few hopes that Sunday's Moscow-backed referendum in the strategic Black Sea peninsula that has been seized by Kremlin troops could be averted or delayed.

President Barack Obama pledged Wednesday to declassify a report on CIA interrogations that sparked a fierce public row between the spy agency and a top senator.

Obama also said that claims that the CIA snooped in on computers used by the Senate Intelligence committee as it probed the agency's interrogations of George W. Bush era terror suspects had been properly handled by chief John Brennan.

U.S. President Barack Obama spoke late Sunday with Chinese President Xi Jinping about ways to peacefully resolve a tense crisis over control of Ukraine's Crimea region, the White House said.

"They affirmed their shared interest in reducing tensions and identifying a peaceful resolution to the dispute between Russia and Ukraine," the White House said in a statement released on Monday.

Sarah Palin offered unsolicited advice Saturday to President Barack Obama on containing Russian aggression, saying "the only thing that stops a bad guy with a nuke is a good guy with a nuke."

The Republican former vice presidential candidate used a predominantly crass tone throughout her appearance at the Conservative Political Action Conference.

President Barack Obama and key European allies expressed "grave concern" Saturday over Russia's actions in Ukraine as Washington warned further military escalation could jeopardize chances of brokering a diplomatic solution to the crisis.

The White House said Obama discussed Ukraine in calls with French counterpart Francois Hollande, British Prime Minister David Cameron and Italian leader Matteo Renzi.

Russia does not want a new Cold War, President Vladimir Putin's spokesman said on Friday, as tensions rose over Russian-backed demands by Crimea to secede from Ukraine.

Dmitry Peskov was asked on a chat show on state television whether he could foresee a return to the clash of ideologies that polarized the world between 1945 and the fall of the Berlin Wall in 1989.

U.S. President Barack Obama on Thursday said he was powerless to stop mass expulsions of illegal immigrants, which prompted one Latino advocacy group to brand him "deporter in chief."

The president said Congress was requiring him to enforce existing immigration laws while balking at passing a comprehensive bill that would offer illegal immigrants a path to citizenship.

Stepping up pressure on Russia, the United States on Thursday slapped visa bans on those Russians and Ukrainians it blames for destabilizing Ukraine and set the stage for more sanctions.

The White House said President Barack Obama was ordering visa bans "in response to Russia's ongoing violation of Ukraine's sovereignty and territorial integrity."

U.S. National Security Adviser Susan Rice will travel to Israel in May to head an American delegation for wide-ranging bilateral talks, the White House said Wednesday.

The announcement came two days after President Barack Obama met with Israeli Prime Minister Benjamin Netanyahu at the White House and they found themselves once again very publicly at odds as they discussed the sensitive issues of Israeli-Palestinian peace talks and Iran's nuclear program.

Russian Foreign Minister Sergei Lavrov on Wednesday resisted Western pressure to meet his Ukrainian counterpart but said talks with the United States and others would continue in coming days, as Moscow and Berlin discussed the “normalization” of the situation in Ukraine.

At the end of a day of intense diplomatic negotiations in Paris, Lavrov left the French foreign ministry without having held a hoped-for meeting with acting Ukrainian foreign minister Andriy Deshchytsya, a member of a government Moscow is refusing to recognize.