Four-day joint naval drills by the South Korean and US military in the Sea of Japan sent a strong message to North Korea, the US command said Thursday.

'These defensive, combined training exercises are designed to send a clear message to North Korea that its aggressive behaviour must stop,' General Walter Sharp, commander of the 28,500 US troops in South Korea, said in a statement.

The aircraft carrier USS George Washington, several destroyers from both navies and more than 200 aircraft were deployed along with 8,000 personnel for the exercises, codenamed Invincible Spirit, which started Sunday and ended Wednesday.

South Korea accuses the Stalinist North of being responsible for the sinking of one of its warships in March.

Meanwhile, military talks between Pyongyang and the US-led UN Command scheduled for Thursday have been postponed, the Yonhap news agency reported, quoting a defence ministry official in Seoul.

The third colonel-level meeting had been convened to discuss the sinking of the Cheonan. Last week, the two sides had agreed to meet Thursday, but had not confirmed the date, the official said.