North Korea's claim that it launched a ballistic missile from a submarine was mostly likely a bluff and the images it released appear photoshopped to overstate the regime's military power, U.S. experts said Tuesday.

Pyongyang state media announced triumphantly on Saturday that a new submarine-launched ballistic missile had been tested successfully, under the personal supervision of the country's leader Kim Jong-Un.

Four U.S. relatives with ties to Lebanon were charged Tuesday with conspiring to illegally ship a large number of guns and ammunition to Lebanon, hidden in supplies for refugees.

Federal agents intercepted cargo containers in March and again last week that were bound for Beirut carrying a total of 152 firearms and 16,000 rounds of ammunition, according to a criminal complaint unsealed Tuesday.

Russia vowed Tuesday it was ready to work with the United States on a host of burning issues but insisted it would not bow to "coercion," as President Vladimir Putin hosted top U.S. diplomat John Kerry. 

On the highest-level U.S. visit to Russia since the conflict in Ukraine erupted in late 2013, Putin met with Kerry at his summer residence in the Black Sea resort of Sochi.

A U.S. Marine Corps helicopter carrying out earthquake relief in Nepal was reported missing on Tuesday with eight personnel on board, officials said.

"The incident occurred near Charikot, Nepal while the aircraft was conducting humanitarian assistance and disaster relief operations," said Major Dave Eastburn, spokesman for US Pacific Command.

Iranian nuclear negotiator Abbas Araghchi said on Tuesday he was "very hopeful" that an accord on Tehran's nuclear program could be reached with world powers ahead of the June 30 deadline.

"Different elements inside and outside of the negotiation chamber can prevent a deal but despite all of this, we will continue the negotiations and we are very hopeful that we can reach a deal before the deadline," he said at the start of a new round of talks in Vienna.

Discontent with American policy toward Iran is behind the last-minute pullout by Saudi King Salman from a summit with U.S. President Barack Obama this week, analysts say.

Obama invited Salman along with five other Gulf rulers to the White House on Wednesday followed by a retreat the following day at Camp David.

The U.S. Senate overwhelmingly passed a resolution Monday calling for Iran to release three American citizens being held in the country.

The non-binding measure, which passed 90 votes to zero, urges the White House to use all tools available to seek and obtain the return of the detained Americans, who include pastor Saeed Abedini, Washington Post journalist Jason Rezaian and former U.S. Marine Amir Hekmati.

Convicted Boston bomber Dzhokhar Tsarnaev has expressed sincere remorse for carrying out the deadly attacks in 2013, a prominent American nun and anti-death penalty campaigner told his trial Monday.

Sister Helen Prejean, who was portrayed in an Oscar-winning performance by actress Susan Sarandon in Hollywood movie "Dead Man Walking," was the final witness called by the defense in its bid to save Tsarnaev from death.

George Zimmerman, the former neighborhood watch volunteer who shot and killed black teen Trayvon Martin in 2012, was injured Monday in a dispute involving a firearm, officials said.

Police in Lake Mary, Florida, said Zimmerman suffered minor injuries from flying glass after a bullet was fired at a window of his car following an altercation with another man.

U.S. President Barack Obama has no immediate plans to visit Cuba but has not ruled out making such a trip "in the year to come," the White House said Monday.

As France's President Francois Hollande touched down in Havana, Obama's spokesman Josh Earnest told reporters who asked if the U.S. leader would follow suit: "I would not rule it out."