The U.S. has taken possession of a North Korean cargo ship for violating international sanctions, a first-of-its-kind seizure that came amid escalating tensions between the two countries over North Korea's nuclear weapons program.

The Wise Honest, North Korea's second-largest bulk carrier, was seized by Indonesian authorities last April as it was transporting 25,000 tons of high-grade coal valued at $3 million to Indonesia.

Officials said the vessel was now in U.S. custody and on its way to American Samoa, and they're seeking a civil injunction against it.

The vessel was owned by a subsidiary of a North Korean shipping company linked to the country's military that is now on a Treasury Department sanctions list. It was used to transport large quantities of coal to China and other countries, and to deliver heavy machinery to North Korea, in violation of U.S. and U.N. sanctions, officials said.

'This sanctions-busting ship is now out of service,' said Assistant Attorney General for National Security John Demers. 'Forfeiting the ship will deprive the North Korean regime of a significant means by which it has evaded sanctions and funded itself.'

The announcement came as Pyongyang conducted its second missile launch in less than a week, escalating tensions with the United States. But U.S. law enforcement officials insisted the two events were not linked.

'We've been pursuing this for months,' said Geoffrey Berman, the U.S. attorney for the Southern District of New York, where prosecutors filed a civil complaint against the ship for violating U.S. sanctions.

The vessel was used by North Korea to ship coal to foreign purchasers from 2016 until April 2018, when Indonesia maritime authorities detained it. To evade sanctions, the ship's operators concealed the origin of its cargo and the countries where it was registered.

Payments for the ship's maintenance and operations were made in U.S. dollars through three unwitting U.S. banks, all in violation of U.S. and U.N. sanctions on North Korea, U.S. officials said.