South Korea and the United States kicked off their largest joint military exercises in five years on Monday, reports AFP.
They commenced it after nuclear-armed Pyongyang warned such drills could be seen as a "declaration of war".
Washington and Seoul have ramped up defence cooperation in the face of growing threats from the North, which has conducted a series of banned weapons tests in recent months.
The US-South Korea exercises, called Freedom Shield, are scheduled to run for at least 10 days from Monday and will focus on the "changing security environment" due to North Korea's redoubled aggression, the allies said.
In a rare move, the Seoul military this month revealed that it and Washington special forces were staging "Teak Knife" military exercises -- which involve simulating precision strikes on key facilities in North Korea -- ahead of Freedom Shield.
All such exercises infuriate North Korea, which views them as rehearsals for an invasion.
It has said its nuclear weapons and missile programmes are for self-defence.
Over the weekend, North Korea fired two "strategic cruise missiles" from a submarine in waters off its east coast, the official KCNA news agency reported Monday.
The agency cited the country's "invariable stand" to confront a situation in which "the US imperialists and the South Korean puppet forces are getting ever more undisguised in their anti-DPRK military maneuvers".
"Pyongyang has military capabilities under development it wants to test anyway and likes to use Washington and Seoul's cooperation as an excuse," said Leif-Eric Easley, a professor at Ewha University in Seoul.
DPRK is the initialism for North Korea's official name, the Democratic People's Republic of Korea.
In a separate statement, North Korea's foreign ministry said the United States was "scheming" to call a UN Security Council meeting on human rights in the reclusive communist state, to coincide with the joint manoeuvres.
"The DPRK bitterly denounces the US vicious 'human rights' racket as the most intensive expression of its hostile policy toward the DPRK and categorically rejects it," the ministry said, according to KCNA.
Last year, the North declared itself an "irreversible" nuclear power and fired a record-breaking number of missiles, with leader Kim Jong Un last week ordering his military to intensify drills to prepare for a "real war".
Bd-pratidin English/Lutful Hoque
