NICE, France - Countries must respect science and international law when it comes to seabed exploitation, which must not become a lawless "Wild West", United Nations Secretary-General Antonio Guterres said Monday at the opening of the third UN Ocean Conference (UNOC3) in Nice, southeastern France.

There must be a balance between justified concerns about environmental impact and the legitimate interest in harnessing resources to support a sustainable ocean-based economy and the transition to green energy, Guterres said. He stressed that future actions must be "grounded in science, guided by precaution, and in line with the rights and obligations enshrined in the UN Convention on the Law of the Sea".

"I support the ongoing work of the International Seabed Authority on this important issue. The deep sea cannot become the Wild West," he added.

Jointly organized by France and Costa Rica, UNOC3 seeks to advance the implementation of Sustainable Development Goal 14 (SDG14): conserve and sustainably use the oceans, seas and marine resources.

Speaking at the opening session, French President Emmanuel Macron also opposed deep-sea exploitation, warning that much of the seabed remains largely unexplored. "It is madness to exploit the deep sea before exploration has even begun... The moratorium on deep-seabed exploitation is an international necessity," Macron said.

"The deep sea is not for sale, no more than Greenland is to take, or Antarctica or the high seas," he said.

In April, US President Donald Trump signed an executive order authorizing deep-sea mining -- a unilateral move that drew criticism from the International Seabed Authority.