SEOUL (AFP) - North Korea on Monday fired two missiles into the sea and vowed to carry out "merciless strikes" against the United States and South Korea, as the allies kicked off joint military drills.
The annual exercises always trigger a surge in military tensions and warlike rhetoric on the divided peninsula, and analysts saw the North's missile tests as a prelude to a concerted campaign of sabre rattling.
South Korea's Yonhap news agency reported the North had fired two short-range missiles into the East Sea ahead of the start of military exercises by Seoul and Washington that have enraged Pyongyang.
"The situation on the Korean peninsula is again inching close to the brink of a war," the official KCNA news agency said, quoting a spokesman for the Korean People's Army (KPA).
"The only means to cope with the aggression and war by the US imperialists and their followers is neither dialogue nor peace. They should be dealt with only by merciless strikes."
The largest element of the drills is Foal Eagle, an eight-week exercise involving air, ground and naval field training, with around 200,000 Korean and 3,700 US troops.
A week-long, largely computer-simulated joint drill - Key Resolve - will also get underway.
Seoul and Washington insist the exercises are defence-based in nature, but they are condemned by Pyongyang as provocative rehearsals for invasion.
The KPA spokesman branded the exercises as "dangerous nuclear war drills for invading the DPRK (North Korea)" and "unpardonable war hysteria of dishonest hostile forces".
"Our revolutionary armed forces will never remain a passive onlooker to this grave situation," the KCNA report said, adding that North Korea would respond in kind to any conventional, nuclear or cyber act of war against it.
"In case even a single shell drops on any place over which the sovereignty of the DPRK is exercised, it will promptly take counteractions."
The Japanese government said it had issued a strong protest to the North given the danger such missile launches posed to aviation and shipping.
Missile tests have long been a preferred North Korean method of expressing anger and displeasure with what it views as confrontational behaviour by the South and its allies. "If there is a particularly sharp escalation, we could see the North orchestrating some kind of clash on the maritime border," said Jeung Young-Tae, an analyst at the Korea Institute for National Unification in Seoul.
Although its nuclear program remains shrouded in uncertainty, Pyongyang is currently believed to have a stockpile of some 10 to 16 nuclear weapons fashioned from either plutonium or weapons-grade uranium.
A new research report by US experts published last month estimated that North Korea could be on track to have an arsenal of 100 nuclear weapons by 2020.
North Korea has carried out three nuclear tests - in 2006, 2009 and 2013. In January, the North offered a moratorium on further tests if this year's joint drills were cancelled - a proposal rejected by Washington as an "implicit threat" to carry out a fourth atomic detonation.
Analyst Mr Jeung said Pyongyang was unlikely to conduct a fourth test just to protest against the exercises. "Nuclear tests carry more significance than that," he said, noting that the North's testing schedule was primarily driven by technical development.