South Korea and the United States kicked off their largest-ever joint air drill on Friday at a time of elevated military tensions with North Korea.

The so-called "Max Thunder" exercise, which is held twice a year, will last until April 25 and involve 103 aircraft and 1,400 service personnel, a South Korean air force spokesman said.

South Korea's defense ministry said Friday it was convinced that three crashed drones recovered in recent weeks were of North Korean origin.

Wreckage of the rudimentary drones was found in three different places, including Baengnyeong island near the rivals' disputed sea border.

Kim Jong-Un was Wednesday "re-elected" as North Korea's leader, state media said, as parliament met in a session closely watched for power shifts in the regime following the shock execution of his once-powerful uncle.

The new parliament also elected members of the powerful National Defense Commission (NDC), appointing Kim's close confidante Choi Ryong-Hae as one of three vice chairmen of the top military decision-making body.

The United States on Tuesday asked North Korea to look at Iran's example, saying it was willing to negotiate with a hostile nation when it is "serious" about its promises.

Amid high tensions between North Korea and its neighbors, Deputy Secretary of State William Burns said that the United States remained firmly opposed to North Korea's nuclear weapons program but was open to diplomacy.

South Korean President Park Geun-Hye called Monday for tighter vigilance against North Korea, days after its leader Kim Jong-Un warned of a "very grave situation" on the peninsula.

At a meeting with top aides, Park noted North Korea had recently threatened a fresh nuclear test, test-fired missiles and lobbed artillery shells across the sea border.

U.S. Defense Secretary Chuck Hagel got a first-hand look at China's new aircraft carrier on Monday as Beijing offered an unprecedented glimpse into its growing military clout.

Hagel praised the ship tour as a promising step forward for a fledgling U.S. dialogue with the often secretive People's Liberation Army (PLA), but the two sides remained deeply divided on cyber-spying and regional territorial disputes.

Japan's defense chief has ordered the armed forces to shoot down any North Korean ballistic missiles that threaten to hit the country, according to media reports.

Defense Minister Itsunori Onodera issued the order on Thursday -- without publicly announcing it -- after North Korea launched two medium-range ballistic missiles on March 26 towards the Sea of Japan (East Sea), Kyodo News and other media said on Saturday, quoting a government source.

North Korea has slammed the South's recent ballistic missile test, calling it a "farce" aimed at showing off Seoul's military strength in the face of threats from Pyongyang.

Seoul said Friday it had successfully test-fired a new ballistic missile capable of carrying a one-ton payload up to 500 kilometers (310 miles), suggesting it could hit any part of the North.

Pentagon chief Chuck Hagel on Sunday warned China against unilateral action to resolve territorial disputes with its neighbors, drawing a parallel with Russia's incursion in Ukraine as he announced two more warships would be sent to Japan.

Seeking to reassure Washington's longtime ally Japan, Hagel's remarks and promise of more missile defense ships came as Tokyo faces a tense row with Beijing over islands in the East China Sea.

North Korea has sacked its commerce minister, according to state-run media Saturday, as its young leader Kim Jong-Un apparently seeks to sideline supporters of his once-powerful uncle who was executed last year.

North Korea's radio broadcaster Pyongyang Broadcasting Station said that new Commerce Minister Kim Kyong-Nam took part in a food festival marking the birth anniversary of the country's founder Kim Il-Sung.