The NSG will consider a draft which is being presented before the 45-nation grouping after amendments following demands by at least 15 countries during the August 21-22 meeting.
Countries like New Zealand and Austria, which are still not satisfied with the revised draft, are expected to voice their concerns over non-proliferation issues.
On studying the draft circulated to them by Germany, the current Chair of the NSG, these countries feel that the amendments in the text are only cosmetic in nature and conditions are not attached.
China, too, appeared on Monday to be joining the sceptic countries when its Communist Party's mouthpiece People's Daily described the Indo-US nuclear deal as a "blow" to n-proliferation.
However, the Chinese Government on Tuesday indicated that it will not block the initiative.
India, on the other hand, has maintained that if conditions are attached to the waiver, it could walk away.
India and the US are hoping that the 45-nation grouping would have a consensus on giving the exemption at this meeting to enable the American Congress some time to have a final vote on the nuclear deal.
Ahead of the meeting, the US has been campaigning hard for the exemption for India, arguing that it would be good for the world.
The NSG works by consensus and even if one country opposes the waiver, the move will be scuttled.
Foreign Secretary Shivshankar Menon, who is in the US, will travel directly to Vienna. He will be joined by R B Grover, Director, Strategic Affairs in the Department of Atomic Energy, and some other officials of the MEA.
Though India is not a member of the NSG, the delegation led by Menon will be camping in Vienna to meet envoys of the NSG countries, if necessary, to make further efforts to persuade them.
Indian officials said that while all efforts will be made to allay the apprehensions of the sceptic countries, India will not accept the waiver if it is laden with conditions.
India says the revised draft should be able to address the apprehensions that some of the countries have.
New Delhi maintains that if any country has any non-proliferation issues, those can be sorted out with them when bilateral agreements are signed.
A day after the editorial in Chinese People's Daily increased anxiety over the fate of the waiver, Beijing expressed hope that the NSG would be able to "strike a balance between nuclear non-proliferation and peaceful use" of atomic energy.
Chinese Foreign Ministry spokesperson Jiang Yu said Beijing has always played a "positive role" at the meetings of the NSG as it believes all countries have the right to develop nuclear energy while observing the obligations of the non-proliferation regime.
China expects the "relevant countries" would be able to "safeguard the effectiveness of the international non-proliferation regime," Jiang said without specifically naming India and the US in this context.
US to push for N-waiver in NSG
With the Nuclear Suppliers Group (NSG) all set to meet in Vienna on Thursday to consider waiver for India, the United States on Tuesday said that it will not "give up the ship" and push forward for the agreement.
State Department Spokesman Sean McCormack said that the United States believed that the deal is in the interests of global non-proliferation efforts and something that is worthy of NSG support.
"We're going to continue to work within the group and work with individual states to try to move it forward," he told the daily press briefing.
"...we're not giving up the ship at all. It's a very tight series of deadlines that were out there, in terms of working this through the international system, working it through our Congress," McCormack said.
He said that the United States will be represented by Undersecretary for Political Affairs Bill Burns and acting Undersecretary John Rood at the NSG meeting in Vienna on September 4 and 5.
The spokesman said that the US will continue to move the case forward and is in touch with other members of the Nuclear Suppliers Group.
"We believe that this is an issue in which the NSG should act and should move forward," McCormack said.
"But, again, there's a lot of hard diplomacy that goes - goes into that in getting a consensus within the group," the senior State Department official said.
When asked whether a "rump" session of the US Congress will be convened to push the Indo-US nuclear deal, McCormack said: "all I can say is we're going to keep pushing forward on it".
He admitted that some member countries of the 45-nation grouping have expressed concerns about the deal and "we have talked to a lot of those various states."
"I am not going to name them, but we have talked to a lot of them. They have announced themselves publicly. You can look it up and what their concerns are," McCormack said.
"We have made the assessment that this is in our interests, it is in the interests of India to develop civilian nuclear energy, while providing some assurances regarding non-proliferation activities," McCormack said.