The NSG began a two-day meeting today in the Austrian capital to consider India's application which is strongly supported by the US.
However, reports from Vienna said that China was leading the opposition to India's membership. Turkey, New Zealand, Ireland, South Africa and Austria are said to be backing the Chinese stand.
Earlier in the day, Prime Minister Narendra Modi got the backing of Mexico during a short visit there after his talks in Washington with President Barack Obama who supported India's case.
In a letter, US Secretary of State John Kerry has made an appeal to NSG member states which are not supportive of India's membership bid, saying they should "agree not to block consensus on Indian admission" to the group when it again meets in Seoul later this month.
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"India has shown strong support for the objectives of the NSG and the global nuclear nonproliferation regime and is a 'like-minded' state deserving of NSG admission," Kerry wrote, according to Bloomberg.
Modi on Monday had visited Switzerland, another member of the NSG which is known to have strong proliferation concerns, and it had announced support to India's candidature.
The NSG looks after critical issues relating to nuclear sector and its members are allowed to trade in and export nuclear technology. Membership of the grouping will help India significantly expand its atomic energy sector.
India has been reaching out to NSG member countries seeking support to its membership. The NSG works under the principle of unanimity and even one country's vote against India will scuttle its bid.