The U.S. military said Monday it had deployed stealth fighters to South Korea as part of an ongoing joint military exercise that has triggered dire North Korean threats of armed retribution.

Two F-22 Raptor fighters arrived in the South on Sunday to participate in the annual "Foal Eagle" exercise that will last until April 30, a spokesman for the U.S. forces in South Korea told Agence France Presse.

A worker was killed and three others were injured Sunday during an industrial accident at a U.S. nuclear power plant that did not release any nuclear material, officials and operators said.

Part of a generator fell as it was being moved out of the turbine building at Entergy Operations Inc's Arkansas Nuclear One in Russellville, the company said in a statement.

Russia warned Friday that a flare-up in tensions between North Korea and the United States could spin out of control, urging all sides involved in the standoff to refrain from muscle-flexing.

"Unilateral actions are being taken around North Korea which manifest themselves in an escalation of military activity," Russian Foreign Minister Sergei Lavrov said.

A former U.S. soldier has been arrested and charged with terror offenses after he allegedly traveled to Syria and joined an al-Qaida-linked rebel group, the Justice Department said Thursday.

Eric Harroun, a 30-year-old army veteran from Phoenix, Arizona, is alleged to have joined a squad of guerrilla fighters from the Al-Nusra Front, training to use rocket-propelled grenades against Syrian government forces.

Defense Secretary Chuck Hagel said Thursday that the United States was "prepared to deal with any eventuality" from North Korea and warned that danger from Pyongyang was on the rise.

"We will unequivocally defend -- we are unequivocally committed -- to that alliance with South Korea as well as our other allies in that region of the world," Hagel told reporters.

U.S. Defense Secretary Chuck Hagel promised "unwavering" support from the United States to its ally South Korea on Wednesday after North Korea severed a military hotline with Seoul.

During a call with his South Korean counterpart Kim Kwan-Jin, Hagel "reaffirmed the strength of the alliance, which has been, and continues to be, instrumental in maintaining stability on the Korean peninsula," Pentagon spokesman George Little said in a statement.

Taiwan is on track to take delivery of 12 anti-submarine aircraft from the United States by mid-2015, a report said Wednesday, as it seeks to beef up its naval defenses against China.

Navy Chief of Staff Vice Admiral Hsu Pei-shan spelt out the timeframe when asked by a lawmaker about a possible delay in the delivery of the aircraft, the state Central News Agency reported.

U.S. President Barack Obama Tuesday named Julia Pierson as the first female chief of the Secret Service, the elite protection branch sullied by a prostitution scandal in Colombia last year.

Pierson, currently Secret Service chief of staff, has worked for the agency, which protects the president and his family and investigates currency counterfeiting and fraud, for 30 years.

Phalange Party leader Amin Gemayel warned on Tuesday that the state of instability the neighboring Syria is going through might be reflected in chaos inside Lebanon, urging the deployment of international peacekeeping forces on the border.

"The prolongation of Syria's conflict will worsen the situation in Lebanon and the social and security conditions of refugees,” Gemayel said in a speech he gave on democracy in the Arab world at the German Marshall Fund of the United States in Washington.

The U.S. administration will appoint U.S. Middle East Envoy David Hale as Washington's Ambassador to Lebanon, media reports said on Tuesday.

Hale will replace current ambassador Maura Connelly when her term ends this year, sources told the pan-Arab daily al-Hayat.