North Korea said it had the right to launch a pre-emptive attack to counter a US-South Korean joint military training drill, its official media reported on Tuesday. US and South Korean troops began military exercises on Monday dubbed Ulchi Focus Lens that are aimed at testing command structures and communications.
The annual exercises have been held without incident since they began in 1975 and the North usually brands them as a prelude to invasion and nuclear war.
But the drills this year are being held with tensions high on the peninsula after North Korea test-fired a barrage of missiles on July 5 and reports last week it may preparing to test a nuclear weapon.
In its KCNA news agency, North Korea said the drills were "an undisguised military threat and blackmail against the DPRK (North Korea) and a war action".
"The Korean Peoples' Army side, therefore, reserves the right to undertake a pre-emptive action for self-defence against the enemy at a crucial time it deems necessary to defend itself," the agency cited an army spokesman as saying.
South Korea has more than 650,000 soldiers in its armed forces, who are supported by about 30,000 US troops on the peninsula. North Korea has a 1.2-million-strong army, mostly stationed near the heavily fortified border with the South.
US television network ABC news last week reported that a US intelligence agency had observed suspicious vehicle movements at a suspected North Korean nuclear test site. It quoted an unidentified State Department official as saying a test was a real possibility.
Other intelligence experts say there is no sign of an imminent test. The report came as six-party talks aimed at getting North Korea to abandon its nuclear weapons programme remain stalled. Pyongyang, angry over a US crackdown on firms Washington suspects of aiding it in illicit activities, refuses to attend. North Korea may be stashing large amounts of illicit money in banks around the world, including in Europe, a senior US official said on Monday. The US crackdown has led a Macau bank to freeze about $24 million in North Korean assets.