WASHINGTON/SEOUL, Aug 29 (Reuters) - President Donald Trump warned on Tuesday that "all options are on the table" as the United States considers its response to North Korea's firing of a ballistic missile over northern Japan's Hokkaido island into the sea.

The test, one of the most provocative ever from the reclusive state, came as U.S. and South Korean forces conduct annual military exercises on the peninsula, angering North Korea which sees them as a preparation for invasion.

North Korea has conducted dozens of ballistic missile tests under its young leader, Kim Jong Un, the most recent on Saturday, in defiance of U.N. sanctions, but firing projectiles over mainland Japan is rare.

Trump, who has vowed not to let North Korea develop nuclear missiles that can hit the mainland United States, said the world had received North Korea's latest message "loud and clear".

"This regime has signalled its contempt for its neighbors, for all members of the United Nations, and for minimum standards of acceptable international behaviour," Trump said in a statement.

"Threatening and destabilising actions only increase the North Korean regime's isolation in the region and among all nations of the world. All options are on the table," he said.

Trump and Japanese Prime Minister Shinzo Abe spoke and agreed that North Korea "poses a grave and growing direct threat to the United States, Japan, and the Republic of Korea, as well as to countries around the world", the White House said.

The Republic of Korea is South Korea's official name.

"President Trump and Prime Minister Abe committed to increasing pressure on North Korea, and doing their utmost to convince the international community to do the same," the statement said.

U.S. stocks opened lower, with the Dow Jones Industrial Average shedding 0.3 percent and the S&P 500 index falling 0.4 percent. The dollar slumped against a basket of currencies while longer-dated U.S. Treasuries were trading higher.

Global markets reacted to the escalation in tension, buying safe-haven assets such as gold, the Swiss franc and the Japanese yen on expectations domestic investors would bring large amounts of currency home in times of uncertainty.

The U.S. disarmament ambassador said Washington still needed to do "further analysis" of the launch, which would be the subject of a U.N. Security Council meeting later on Tuesday.

"It's another provocation by North Korea, they just seem to continue to happen," U.S. envoy Robert Wood told reporters in Geneva before a session of the U.N.-sponsored Conference on Disarmament.

North Korean envoy Han Tae Song told the session the United States was driving the Korean peninsula "towards an extreme level of explosion" by deploying strategic assets and conducting nuclear war drills.