As massive efforts are underway by India and the United States to get New Delhi [Images] a waiver from the Nuclear Suppliers Group, they are faced with a particularly challenging task of convincing at least four member countries who have reservations to such a proposal.

New Zealand [Images], Austria, Ireland and Switzerland [Images] are seen as the difficult countries, which will require some hard work to convince them before the August 21-22 meeting of the 45-nation NSG, sources said in New Delhi on Thursday.

All the four countries have strong positions with regard to non-proliferation issues and insist that such an exemption should not be given to a country which is not a member of the NPT.

They are expected to raise tough questions at the meeting.

While efforts have been made to convince them, they are yet to relent, the sources said.

NSG works by consensus and even if one country opposes the grant of waiver, it will put India's case in jeopardy. India is making efforts to garner their support, which are being supplemented by the US.

The US has launched a major campaign to muster support of the NSG countries, with President George W Bush [Images] himself sending letters to various countries in this regard.

US Secretary of State Condoleeza Rice is also calling up her counterparts in various NSG countries to persuade them to support the initiative, sources said.

Besides, senior US officials are visiting NSG countries.

The Bush administration has also directed its envoys in 45 member countries of NSG to keep talking to the host governments to muster support, the sources said.

India, on its part, has also deputed some of its ministers and senior officials to various countries to lobby support.

Both Washington and New Delhi are telling the NSG countries that India's entry into the nuclear mainstream will strengthen the non-proliferation system rather than weakening it as apprehended by some nations.