U.S. First Lady Michelle Obama on Saturday denounced as an "unconscionable act" the kidnapping of more than 200 Nigerian schoolgirls by Islamic militants as a mobilized international community helped with the search effort.

For the first time standing in for President Barack Obama on his weekly Saturday morning address, she said they were both "outraged and heartbroken" over the mass abduction from a school dormitory in a remote corner of northern Nigeria last month.

A car trailed an official motorcade that was carrying the daughters of U.S. President Barack Obama on Tuesday, sparking a brief lockdown at the White House.

The Secret Service, which is in charge of the president's security, said the vehicle followed the motorcade past a security barrier about 200 meters (650 feet) from the White House.

The United States secured long term access Monday to a military base in Djibouti that it uses to launch counter-terrorism missions, including drone strikes, in Yemen and the Horn of Africa.

U.S. President Barack Obama and his Djibouti counterpart Ismail Omar Guelleh announced the renewed "long term lease" on Camp Lemonnier to reporters as they met at the White House.

Dozens of specialists from the U.S. Central Intelligence Agency and Federal Bureau of Investigation are advising the Ukrainian government, a German newspaper reported Sunday.

Citing unnamed German security sources, Bild am Sonntag said the CIA and FBI agents were helping Kiev end the rebellion in the east of Ukraine and set up a functioning security structure.

Russia and the United States stepped up their rhetoric over the spiraling crisis in Ukraine, as pro-Moscow militants shored up control of key buildings in the country's increasingly chaotic east Wednesday.

President Vladimir Putin threatened that U.S. sanctions against Moscow could harm Western energy interests in Russia, which the West blames for stoking the worst confrontation since the end of the Cold War.

The United States warned Wednesday it was "actively preparing" new sanctions to hit Russia if critical Ukraine talks do not produce concessions from Moscow.

U.S. officials privately signaled they had little hope that the Geneva talks between Russia, Ukraine, the European Union and Washington would make significant progress.

U.S. Vice President Joe Biden vowed Friday it would work with Ukraine and other allies to prevent countries like Russia from using energy as a "political weapon."

In a telephone call with Ukrainian Prime Minister Arseniy Yatsenyuk, Biden said aid from the United States and other countries would help Ukraine "meet its most pressing needs," the White House said in a statement.

The White House said Wednesday it was disappointed by "unhelpful" actions by both Israelis and Palestinians that threaten to tear apart a U.S.-led peace effort.

Secretary of State John Kerry's bid to save peace talks is in peril after Israel announced plans for new settlement building and the Palestinians took steps towards seeking international recognition.

A man who opened fire on the White House with an assault rifle after telling friends he was on a mission from God to kill President Barack Obama was jailed for 25 years on Monday.

Oscar Ramiro Ortega-Hernandez drove more than 2,000 miles (3,200 kilometers) to the US capital from his home in Idaho to carry out his November 2011 attack.

The White House said Tuesday it is "very disappointed" that Saudi Arabia has denied a Jerusalem Post reporter's visa to cover President Barack Obama's visit to the kingdom later this week.

Deputy national security adviser Ben Rhodes said the White House made clear to the Saudis the importance that the reporter have access to cover the trip.