The White House on Wednesday dismissed Republican criticism of President Barack Obama's handshake with Cuban leader Raul Castro at Nelson Mandela's memorial service.

Obama has faced a backlash from Republican rivals after exchanging pleasantries with Castro, the leader of a Communist-run country that has been bitterly estranged from the United States since 1961.

President Barack Obama on Thursday defended his nuclear diplomacy with Iran before an audience of Israeli diplomats and senior members of the U.S. Jewish community and officials.

At a White House Hanukkah reception, Obama said that it was important for the United States to test Iran's intentions, and pledged to keep working for a comprehensive deal to deprive Tehran of a nuclear weapon.

The White House said Monday that it did not consider peaceful demonstrations in Ukraine as attempts at a coup, and called violent suppression of protests by police unacceptable.

"We certainty don't consider peaceful demonstrations coup attempts," said White House spokesman Jay Carney after Ukrainian Prime Minister Mykola Azarov said the protests bore all the hallmarks of a coup.

White House reporters and photographers on Thursday accused top officials of deliberately blocking access to President Barack Obama and of substituting its own "visual press releases" for independent news coverage.

In a letter to White House spokesman Jay Carney, the White House Correspondents Association (WHCA) and other news organizations said the practice belied the administration's frequent claims to a new level of transparency.

The United States has ruled out apologizing to Afghanistan for "mistakes" made during the 12-year war and denied claims in Kabul that such a mea culpa was being drafted.

The stern comments in Washington came after Afghan leader Hamid Karzai's spokesman said President Barack Obama planned to write a letter acknowledging that American military errors had caused civilian casualties.

Two U.S. Secret Service agents have been removed from President Barack Obama's security detail for alleged misconduct, The Washington Post reported late Wednesday.

The move came a year after the agency was involved in a prostitution scandal in Colombia.

The White House warned U.S. lawmakers Tuesday that tightening sanctions on Iran could box America into a "march to war" and derail a diplomatic push to limit Tehran's atomic program.

The warning marked a significant toughening of President Barack Obama's stance towards skeptical U.S. lawmakers as he prepares to resume high-stakes nuclear diplomacy with Iran later this month.

A U.N. human rights body urged the United States Monday to adjust its intelligence gathering which has outraged America's allies worried by U.S. snooping.

"There has got to be progress made toward some mechanism -- even given states' legitimate need to work for their security -- that is not invasive in terms of individual rights," said Felipe Gonzalez, the head of the Inter-American Commission on Human Rights.

The National Security Agency stopped spying on German Chancellor Angela Merkel and other world leaders after the White House learned of the snooping, the Wall Street Journal reported Monday.

President Barack Obama learned of the electronic surveillance in an internal review he ordered at mid-year, the Journal reported, citing unnamed U.S. officials.

U.S. President Barack Obama and his wife Michelle welcomed Pakistani schoolgirl activist Malala Yousafzai to the Oval Office on Friday.

On the day she was passed over for the Nobel Peace Prize, the Obamas hailed Malala, 16, for her "inspiring and passionate" work on behalf of girls in Pakistan.