Ratification of the treaty's text -- first adopted in June 2023 after years of negotiations -- was a "historic step towards protecting the world's oceans and preserving the delicate balance of our planet's ecosystem," said Costas Kadis, the EU oceans commissioner.

He called on all countries to follow suit.

Cyprus, Finland, Hungary, Latvia, Portugal and Slovenia along with the EU submitted their instruments of ratification to the United Nations, the European mission to the UN said in a statement.

France and Spain had already done so earlier this year.

That brings the number of ratifications to 29 -- still far short of the 60 required for the treaty to enter into force.

The NGO coalition High Seas Alliance hailed the ratifications as a "major step forward."

But treaty supporters "need to up the political pressure to reach 60 ratifications," director Rebecca Hubbard said in a statement.

France is hosting a UN conference on the oceans June 9-13 in Nice, and its "number one" priority is to obtain the ratifications needed, Jerome Bonnafont, the French ambassador to the United Nations, said this week.

A ceremony is scheduled for June 9 in Nice in a bid to approach that threshold.

The landmark treaty aims to protect marine ecosystems vital to humanity, threatened by multiple forms of pollution, in international waters covering almost half the planet.

In particular, it provides for the creation of marine protected areas where certain activities could be restricted.

This could include fishing or mining, which also depend on other international organizations.