South Korea and the United States have agreed a new nuclear pact allowing Seoul to expand its civil atomic energy program, wrapping up more than four years of negotiations, a report said Wednesday.

A signing ceremony will be held at 4:15 pm (0715 GMT) in Seoul, a South Korean foreign ministry official said without revealing contents of the deal.

President Barack Obama called on Iran help find a political solution in crisis-torn Yemen, accusing the Islamic republic of contributing to the conflict there.

Washington has accused Tehran of supplying arms to Huthi rebels who have seized power in Yemen, triggering a month-long Saudi-led Arab air campaign that has increased the risk of a regional conflict.

The United States welcomed Tuesday news that Poland is planning to buy the U.S.-made Patriot missile system in an unprecedented revamp of its military in a deal worth up to $5 billion.

"Poland is a stalwart NATO ally, and its defense modernization program... directly fortifies the military strength of the alliance," State Department acting spokeswoman Marie Harf said in a statement.

Turkey and the United States voiced hopes Tuesday that 2015 could be the year when a long-elusive diplomatic solution is finally found to the decades-old division of Cyprus.

"This is a problem that just has gone on for far too long, and it is begging for international efforts to try to help bring about a resolution, a lasting settlement," U.S. Secretary of State John Kerry said as he met with his Turkish counterpart.

The United States blacklisted two top leaders of Somalia's Shebab on Tuesday, a day after the Islamist group killed seven people, including four U.N. workers, in a huge bus bombing.

Ahmed Diriye, who took over as the militant group's leader in September 2014, and intelligence chief Mahad Karate, were both designated as terrorists by the State Department.

The mayor of Baltimore promised Monday to thoroughly investigate the death of an African American man who died after an arrest that lawyers say left him with severe neck injuries.

The case is the latest in a long series of deaths that critics say demonstrates officers' racial bias and an over reliance on force when dealing with suspects.

The Philippines voiced alarm Monday about Chinese "aggressiveness" in disputed regional waters as it launched giant war games with the United States that were partly aimed as a warning shot to Beijing.

Philippine military chief General Gregorio Catapang released what he said were satellite photos of intense recent Chinese construction over seven reefs and shoals in the Spratly archipelago of the flashpoint South China Sea.

The United States on Sunday condemned the "brutal mass murder" of 30 Ethiopian Christians in Libya following a video released by Islamic State militants purportedly showing their execution.

The 29-minute IS video appears to show militants holding two groups of captives, described in text captions as "followers of the cross from the enemy Ethiopian Church".

Iran's Ayatollah Ali Khamenei urged his armed forces Sunday to increase their "defensive preparedness," denouncing a U.S. warning that military action is an option if there is no nuclear deal.

In a speech to commanders and troops, the supreme leader said "the other side with insolence threaten us all the time," denying Iran was seeking an atomic bomb and insisting its military doctrine is defensive.

Convicted Boston Marathon bomber Dzhokhar Tsarnaev must face death for the attack that killed three people and wounded 254, prosecutors will argue when a court this week begins weighing up his fate. 

The sentencing phase of Tsarnaev's high-profile trial begins Tuesday in the city, just days after the parents of a young boy killed in the dual blasts on April 15, 2013 asked for the death penalty to be dropped.