SEOUL, SOUTH KOREA: North Korea has reacted to the start of US-South Korean war drills with its typical fiery rhetoric. But recent missile and nuclear tests by the North give the usual threats an added weight.

Annual military drills between Seoul and Washington always rile Pyongyang, which calls the defensive drills a rehearsal for an invasion. This year's drills began Wednesday.

The North's military said Thursday it will "mercilessly foil the nuclear war racket of the aggressors with its treasured nuclear sword."

It says its reaction will be the toughest ever but didn't elaborate.

There is renewed worry in Seoul and Washington because North Korea test-launched a new intermediate missile in February. It also conducted two nuclear tests last year.

South Korea's military says it will "resolutely" punish North Korea if provoked.