An aircraft carrier the US Navy said was steaming toward the Korean Peninsula amid rising tensions has not yet departed, a US defence official has acknowledged.

The navy on 8 April said it was directing a naval strike group headed by the USS Carl Vinson super carrier to "sail north," as a "prudent measure" to deter North Korea.

Pentagon chief Jim Mattis on 11 April said the Vinson was "on her way up" to the peninsula.

President Donald Trump the next day said: "We are sending an armada. Very powerful."

But a defence official told AFP that the ships were still off the northwest coast of Australia. A navy photograph showed the Vinson off Java over the weekend.

"They are going to start heading north towards the Sea of Japan within the next 24 hours," the official said on condition of anonymity.

The official added that the strike group would not be in the region before next week at the earliest - it is thousands of nautical miles from the Java Sea to the Sea of Japan.

At the time of the strike group's deployment, many media outlets said the ships were steaming toward North Korea, when in fact they had temporarily headed in the opposite direction.

The United States increased its rhetoric ahead of North Korea's military parade and failed missile launch over the weekend, and Vice President Mike Pence yesterday declared that the era of US "strategic patience" in dealing with Pyongyang was over.

North Korean leader Kim Jong-un responded with his own warnings and threatened to conduct weekly missile tests.

It was not clear if the issue was the result of poor communication by the navy, but some observers were critical.

Joel Wit, a co-founder of the 38 North programme of the US-Korea Institute at Johns Hopkins University, said the matter was "very perplexing" and fed into North Korea's narrative that the US is all bluster and does not follow through on threats.

"If you are going to threaten the North Koreans, you better make sure your threat is credible," he said.

"If you threaten them and your threat is not credible, it's only going to undermine whatever your policy toward them is."

The strike group has been conducting drills with the Australian navy in recent days, the US official said, though it scrapped a planned port visit in Australia as a result of the new orders.