Pakistan has expressed serious concern over finalization of a nuclear deal between the United States and India, saying it would have destabilizing impact on regional stability.

US President Barack Obama and Indian Prime Minister Narendra Modi said the two countries have achieved a "breakthrough" over the civil nuclear deal, six years after it was signed. They reached the understanding during President Obama's visit to India concluded on Tuesday.

"The operationalization of India-US nuclear deal for political and economic expediencies would have a detrimental impact on deterrence stability in South Asia," Pakistan's top security adviser said.

"Pakistan reserves the right to safeguard its national security interests," Sartaj Aziz said in a statement late Tuesday.

He said Pakistan values its relations with the United States and expects it to play a constructive role for strategic stability and balance in South Asia.

Pakistan also opposed permanent seat to India in the UN Security Council after President Obama supported New Delhi's move to seek the seat.

"Proposals to add new centers of privilege in the Security Council run counter to these collective objectives of Security Council reform; and have no rationale in this age of democracy, inclusiveness and accountability," Aziz said.

Pakistan, he said, supports a reformed Security Council that corresponds to the positions and collective interests of all member states, not just a few.

"Pakistan, along with a large majority of UN member states, favours a comprehensive reform of the Security Council to make this principal organ of the United Nations more representative, democratic, effective, transparent and accountable," Aziz said.

"A country, in violation of United Nations Security Council resolutions on matters of international peace and security, such as the Jammu & Kashmir dispute, by no means qualifies for a special status in the Security Council," the Pakistani adviser said.

Pakistan also contested suggestion to grant membership of the Nuclear Suppliers Group to India.

"Pakistan is opposed to yet another country-specific exemption from NSG rules to grant membership to India, as this would further compound the already fragile strategic stability environment in South Asia, would further undermine the credibility of NSG and weaken the nonproliferation regime," Aziz said.

He said Pakistan remains opposed to policies of selectivity and discrimination, adding Pakistan is not averse to civil nuclear cooperation and NSG membership for Non-NPT states provided it is based on the principles of nondiscrimination and objective nonproliferation criteria.