The U.S. State Department released over 4,000 more of the emails former secretary of state Hillary Clinton kept on a private server Monday and revealed that some 150 others have been retroactively classified.

Reporters and Clinton's rivals as she campaigns for the 2016 Democratic presidential nomination began scouring 7,000 additional pages of messages from the mails she handed over earlier this year after coming under fire for operating the unofficial server.

Wisconsin Governor Scott Walker, who is seeking the Republican nomination for the White House, said Sunday that building a wall between the U.S. and Canada was a "legitimate" idea to explore.

Immigration is a hot-button topic in U.S. politics and Donald Trump, the leading Republican contender, has added fuel to the fire by promising to have Mexico pay to build a wall between the United States and its southern neighbor, angering many Hispanics.

Caroline Kennedy, the U.S. ambassador to Japan and daughter of late president John F. Kennedy, was criticized on Tuesday for using private email for official business.

The latest revelations about a high ranking diplomat were given greater resonance in the light of the scandal hanging over former secretary of state Hillary Clinton.

President Barack Obama wrote in a letter to Congress that the U.S. will uphold sanctions targeting Iran's non-nuclear activities, such as its support for Hizbullah.

Obama promised Democratic lawmakers that the U.S. will continue to keep economic pressure on Iran — and keep military options open — if his administration's nuclear deal with Tehran goes through.

The White House said Tuesday it had hired its first openly transgender official, a move which supporters said underscored the administration's drive against inequality.

Officials said former activist Raffi Freedman-Gurspan began work on Tuesday in a team that recruits personnel to serve the president.

President Barack Obama's administration vowed to press ahead with a half-billion-dollar mission to train Syrian opposition fighters Tuesday, despite fears that its initial failures have dented U.S. credibility. 

After the routing of a 54-strong U.S.-trained force by al-Qaida allied rebels, Pentagon spokeswoman Commander Elissa Smith told Agence France Presse there was no plan to pause or scale back the program.

Republican presidential frontrunner Donald Trump on Sunday refused to apologize for a crude attack on a female Fox News journalist that sparked widespread outrage, insisting he was misunderstood.

The brash billionaire -- who is leading a packed Republican field of White House hopefuls -- found himself at the center of controversy after seeming to suggest that Megyn Kelly, one of the moderators of last week's presidential debate, asked him tough questions because she was menstruating.

Republican presidential frontrunner Donald Trump on Sunday refused to apologize for a crude attack on a female Fox News journalist that sparked widespread outrage, insisting he was misunderstood.

The brash billionaire -- who is leading a packed Republican field of White House hopefuls -- found himself at the center of controversy after seeming to suggest that Megyn Kelly, one of the moderators of last week's presidential debate, was tough on him because she was menstruating.

President Barack Obama has warned that any possible rejection by the Congress of the Iran nuclear deal, would force the U.S. to attack Iran, a move that could lead to a Hizbulalh retaliation against Israel.

"It would be destructive both to the U.S. and to Israel," Obama told Jewish leaders on Tuesday, according to Israeli media reports.

U.S. President Barack Obama has extended the national emergency with respect to Lebanon that was declared in Executive Order 13441 of August 1, 2007.

He said in a statement released by the White House on Wednesday that “the national emergency is to continue in effect beyond August 1, 2015.”