The treaty between Kazakhstan, Uzbekistan, Kyrgyzstan, Tajikistan and Turkmenistan with the full blessing of China and Russia was signed on Friday .
Officials from the five states signed the treaty in Semipalatinsk, a town in northern Kazakhstan near the now-defunct testing ranges where the Soviet Union exploded more than 400 atom bombs.
Nuclear weapon free-zone treaties usually require the world's five officially recognised nuclear powers - the US, Britain, France, China and Russia - to sign an accompanying "protocol" pledging to respect the pact.
British, French and US objections centre on a loophole in the treaty, which could - hypothetically - allow Russia to transport or even deploy nuclear weapons across the region under provisions of an older security agreement.
The Western countries say that this loophole undermines one of the new pact's key provisions.
China and Russia have supported the treaty.
In a statement read out by a UN official during the signing ceremony, Kofi Annan, the UN secretary general, said the occasion "marks another step" towards agreeing on a more comprehensive treaty.
“I note that some nuclear weapon states continue to be concerned about aspects of the Central Asian Nuclear-Weapon-Free Zone Treaty," Annan said.
"I would therefore urge the five Central Asian states to engage with the nuclear weapons states with a view to bridging the differences and ensuring the treaty's effective implementation."
China and Russia sent ambassadors to the ceremony while envoys from the United States, Britain and France stayed away.
Jozef Goldblat, a senior researcher of the United Nations institute for disarmament research said: "They objected to article 12 which speaks about the validity of similar treaties signed before this one... This is why they abstained from signing the protocol."
The older treaty which has caused concern is the 1992 Tashkent Treaty, a collective security pact between former Soviet states, Goldblat said.
Russia has in the past interpreted that accord as allowing it to deploy nuclear weapons in Central Asia in a crisis.
Although there was no immediate official comment from the three Western nuclear powers, one Western diplomat, speaking on condition of anonymity, said the Western powers supported such zones but felt it was "premature" to sign the treaty without further talks.
The treaty signed on Friday took nine years to negotiate - partially a reflection of the low level of cooperation between the five "Stans".
But the five nuclear powers, who are also permanent members of the UN security council, had not been invited to discuss the treaty with the Central Asian states since 2002, the diplomat said.
Asked about the disagreement with the Western powers, Kasymzhomart Tokayev, the Kazakh foreign minister said: "I don't think there are any particular contradictions.
"In my speech I invited the permanent members of the UN security council to continue work with us on the text of the protocol."