The treaty, which opened for signature in 2006, is to enter into force Saturday.

"The Secretary General welcomes the entry into force of the Treaty on a Nuclear-Weapon-Free Zone in Central Asia," his spokeswoman Michele Montas said in a statement.

Ban noted that this would be the first nuclear-weapon-free zone to be established in the northern hemisphere and will also encompass an area where nuclear weapons previously existed.

The treaty bans nuclear weapons within the respective territories of the zone, including the acquisition, possession, placement, testing and use of such arms.

First formally proposed by Uzbek President Islam Karimov in 1993, the pact has now been ratified by all five Central Asian states.

The five, all former Soviet republics, are: Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan and Uzbekistan.

After the Soviet Union's 1991 collapse, the five republics all assented to the return of Soviet-made nuclear weapons to Russia.

Other such nuclear-free zone treaties include one established in 1967 for Latin America and the Caribbean, the 1985 South Pacific treaty, the 1995 Southeast Asia treaty and the 1996 Africa treaty.

In addition, Mongolia has a self-declared nuclear-weapon-free status.

The Antarctic Treaty, the Outer Space Treaty and the Seabed Arms Control Treaty also ban nuclear weapons in the relevant geographical areas.