"I must express my deep concern," said ISA chief Leticia Carvalho, who insisted that her international agency holds an "exclusive mandate" to approve or reject such activities.

A unilateral agreement "would constitute a violation of international law," undermining multilateral efforts to peacefully regulate the world's seabeds, she said.

Conservation groups adamantly oppose seabed mining, which they say could devastate vital but poorly understood marine systems.

Greenpeace slammed the Metals Company announcement as "a slap in the face to international cooperation."

Created by the UN Convention on the Law of the Sea (Unclos), the ISA, an autonomous international organization, was designed to protect seabeds in international waters and to regulate mining.

The United States is not a member of the ISA nor of Unclos.

"All exploration and exploitation activities in the area must be carried out under the authority's control," Carvalho insisted as the ISA's governing council wound up a meeting in Kingston, Jamaica.

"This remains the only universally recognized, legitimate framework," she said.

The Metals Company of Canada (TMC), which hopes to become the first company allowed to excavate seabeds in international waters, said Thursday it would seek authorization from the Trump administration, which has shown intense interest in finding new sources of rare metals.

The company said it will submit, via its subsidiary Nori, a request for US approval under a 1980 law establishing US rules for international seabed exploitation.

Mining companies want to scrape vast sections of the Pacific Ocean seabed for metals such as nickel and cobalt, which are used in electric car batteries and other electronics.

TMC invested more than half a billion dollars over the past 10 years to "understand and responsibly develop" mining in the Pacific and is ready to begin commercial operations, the firm's CEO Gerard Barron told a conference call.

The company had originally said it planned in June to go to the ISA to request approval of its mining plans.

But after denouncing the "repeated failure" of the agency to finalize a global mining code regulating such activities, TMC said Thursday that it would turn to the United States.

CEO Gerard Barron said he has been given encouragement in meetings at the White House and with American lawmakers, and said the US path would give the company its best chance to obtain a permit expeditiously.

Debate over the global mining code has gone on for more than a decade. Calls to pause deep-sea mining have meantime been growing, not waning, amid fears of irreversible damage to the undersea environment.

TMC has conducted extensive exploratory work in an area of the Pacific between Mexico and Hawaii viewed as rich in so-called polymetallic modules.