Warnings, threats and accusations continue to feed tensions on the Korean peninsula.
South Korea has referred North Korea to the UN Security Council over the sinking of one of its warships in March.
The South says the rest of the world must act firmly against its northern neighbour and convince it to drop its nuclear programme.
An international investigation has concluded that the Cheonan, a South Korean corvette, was sunk by a North Korean torpedo. The attack left 46 sailors dead.
The United States has said it will carry out joint navy manoevres with South Korea, although it has hinted that these may wait until the UN has acted.
As for North Korea, it continues to deny the accusations against it. State television declared that Washington has ulterior motives and fabricated the investigation. It also warned that the joint naval drills were “a prelude to all-out war”.