UN chief Ban Ki-moon on Thursday called for new steps to achieve a nuclear-free world, ahead of next week's international day against nuclear tests.

"We urgently need new progress in achieving a world free of both nuclear tests and nuclear weapons," Ban said, urging the remaining states to ratify the Comprehensive Nuclear-Test-Ban Treaty, whose entry into force has been stalled for years.

"Current voluntary moratoriums on nuclear weapon tests are valuable, yet they are no substitute for a global ban," he said.

The CTBT "is a major element of the international disarmament and non-proliferation regime, and it deserves the active support of all states," said Ban.

The treaty, which bans nuclear blasts for military or civilian purposes, was drawn up in 1996 and has so far been signed by a total 182 countries and ratified by 154.

However, nine states whose backing is key in order for the CTBT to enter into force -- including China, North Korea, Iran, Israel and the United States -- have yet to ratify the treaty.