President Barack Obama called Ukraine's president-elect Petro Poroshenko on Tuesday and offered him "the full support of the United States."

Obama said the United States would assist Ukraine as Poroshenko "seeks to unify and move his country forward," the White House said.

U.S. President Barack Obama congratulated Narendra Modi and said he was looking forward to working with him after he was sworn in as Indian prime minister on Monday.

"As the president and prime minister agreed in their call after the election, as the world’s two largest democracies, India and the United States share a deep bond and commitment to promoting economic opportunity, freedom, and security for our people and around the world," a White House statement said.

President Barack Obama was back in Washington on Monday after a lightning 32-hour trip to Afghanistan to visit U.S. troops.

Monday is Memorial Day in the United States, when military war dead are remembered and military personnel and veterans are honored. The president is scheduled to host a White House breakfast for veteran groups with top military brass in attendance, the White House said.

As he ponders leaving some troops in Afghanistan after longest U.S. war, Barack Obama harkens back to the September 11, 2001 attacks to justify more than a decade of sacrifice.

Whether the U.S. president is also using that imagery to justify longer U.S. military involvement in Afghanistan, senior political aides will not say.

U.S. President Barack Obama hailed "courageous" Ukrainians who went to the polls Sunday in a presidential vote that Washington and the West hope will bring stability back to the country after months of turmoil.

"Despite provocations and violence, millions of Ukrainians went to the polls throughout the country," the White House quoted Obama as saying.

President Barack Obama swooped out of the night sky into Afghanistan Sunday on a surprise visit, to honor the sacrifices of the soldiers of America's longest war, seven months before he ends the combat mission for good.

Obama, who normally brings cities to a standstill when he moves around, slipped out of the White House and boarded a darkened Air Force One after night fell on Saturday and flew unannounced across the globe, before making a high-speed landing at Bagram Air Base outside Kabul on his fourth visit to Afghanistan as president and his first since 2012.

U.S. Secret Service personnel sprang into action Friday outside the White House when a man stripped naked in what appeared to be a bizarre form of protest.

On one of the hottest days of the year so far in the U.S. capital, where temperatures hit at least 26 degrees Celsius (78 Fahrenheit), the man ambled up to Secret Service officers at the gate of the White House and then took off all his clothes.

Washington is closely monitoring an upsurge of violence in Libya, but has not decided yet whether to order the closure of its embassy in Tripoli, a U.S. official said Monday.

Libyan gunmen stormed parliament in southern Tripoli on Sunday, hot on the heels of an anti-Islamist offensive launched by a rogue general in the eastern city of Benghazi.

President Barack Obama announced Monday that the United States would offer an extra $50 million to help tackle a growing refugee crisis spawned by fighting in South Sudan.

The money will be sent to international and non-governmental organizations and be used to pay expenses of the State Department's Bureau of Population, Refugees, and Migration in the region, Obama said in a memorandum.

U.S. President Barack Obama called India's outgoing Prime Minister Manmohan Singh on Saturday to convey "gratitude" for "his critical role" in deepening ties between the two allies.

India is a key part of Obama's policy of pivoting U.S. power to Asia. On his 2010 visit, Obama called the budding strategic relationship between the world's two largest democracies "one of the defining partnerships of the 21st century."