US authorities were prepared Tuesday to seize $100 million worth of oil from a tanker anchored off the Texas coast after Iraq's government told a court the oil was taken illegally from the country's Kurdish region.

The United Kalavrvta tanker remained in international waters about 60 miles (100 kilometers) offshore, but if it offloads its million-barrel crude oil cargo to smaller vessels that enter US waters, marshals will enforce a federal judge's order and seize the cargo, a spokesman said.

"We haven't carried it (the order) out yet. Right now, we're monitoring the situation," US Marshals Service spokesman Dave Oney told AFP.

Late Monday, Houston judge Nancy Johnson ordered the seizure after Iraq's oil ministry petitioned the court to block its delivery to the buyer, which, according to a court filing, is Talmay Trading, a company registered in the British Virgin Islands.

The petition said the Kurdistan Regional Government (KRG) illegally pumped and exported the oil from northern Iraq through Turkey, where it was loaded on a vessel at Ceyhan in late June.

"The Ministry of Natural Resources of the KRG which loaded the cargo is not the owner of the oil nor does it have any title on the oil, which has been illegally misappropriated," the Iraqi complaint said.

The vessel arrived near Galveston Bay last week, but no effort has been made to offload it.

The ship, which is carrying more than a million barrels of crude oil, is required to give 96 hours' notice if it plans to offload the cargo, Oney said.

The fighter over the tanker pits Iraq's central authorities against the autonomous Kurdistan regional government in a high-stakes political feud that could help determine whether Iraq remains a single country or divides along ethnic and sectarian lines.

The central government and Kurdish leaders have long been at loggerheads over how to share power and oil revenues.

Kurdish territory in the north is believed to hold large oil reserves and if the regional government manages to successfully deliver oil shipments abroad, it could encourage a push for independence, analysts say.

US officials said Washington has always favored oil sales being overseen by the central government in Baghdad.

"It's US policy that we oppose the selling of oil outside of the central government of Iraq," State Department spokeswoman Jen Psaki told reporters.