India has summoned the US ambassador to Delhi after comments he made over India's relations with Iran.
Mr Mulford expressed 'sincere regrets'
US Ambassador David Mulford had warned that a deal giving India US nuclear technology could collapse if India does not back a UN motion against Iran.
He was told his comments were "inappropriate and not conducive" to US-India relations, India's foreign ministry said on Thursday.
Mr Mulford earlier said his remarks were taken out of context.
The US State Department said Mr Mulford was voicing his "personal opinion".
The US is pursuing action against Iran which it suspects of trying to develop a nuclear weapons programme.
Mr Mulford told the Press Trust of India (PTI) news agency on Wednesday that the US was keen to have India's support when UN atomic watchdog, the International Atomic Energy Agency (IAEA) meets to discuss Iran.
"If [India] opposes Iran having nuclear weapons, we think they should record it in the vote."
India's failure to do so, he said, would have a "devastating" effect on US Congress members who have yet to approve the nuclear deal.
"I think the initiative will die in the Congress. Not because the administration would want it to, but the Congress will... so I think this is part of the calculation that India has to keep in mind," Mr Mulford said.
Mr Mulford also said India had not met "test of credibility" in showing a clear separation of its civilian and military nuclear programmes - a key condition of the technology-sharing deal agreed last year, the PTI said.
Mr Mulford was summoned by India's Foreign Secretary, Shyam Saran, on Thursday afternoon and told that his comments were "inappropriate and not conducive to building a strong partnership between the two democracies," a foreign ministry statement said.
India wants to use nuclear power to meet its energy needs
It said that the ambassador was informed that India's vote on any possible resolution on the Iran nuclear issue at the International Atomic Energy Agency (IAEA) would be determined by India's own judgement of the merits of the case.
"The ambassador expressed his sincere regrets, saying that his remarks had been taken out of context," the foreign ministry statement said.
India has rejected attempts to tie its stance on Iran to the deal with the US.
Washington agreed last year to share advanced civilian nuclear technology with Delhi, lifting sanctions triggered by India's nuclear tests in 1998.
State department spokesman Sean McCormark said on Wednesday that Mr Mulford was "reflecting" the "very strongly held feelings about Iran" in the Congress about the Iran issue.
"Ultimately, how India votes on this matter is going to be a decision of the Indian government. They voted to find Iran in non-compliance the last time around and we certainly would encourage and hope that they vote for referral this time around," he said.
Mr McCormack also sought to separate the civilian nuclear deal with how India votes on the Iran issue.
"We deal with the Indian government on these two issues as separate issues. Certainly, they come up in the same conversations," he told reporters in Washington.
Correspondents say Mr McCormack's comments are a move to defuse any potential political and diplomatic row that could erupt between the two countries ahead of President George Bush's visit to India in March.
One of the key allies of the ruling Congress party-led coalition, the Communist Party of India (Marxist) has also demanded the government must clarify its stand after Mr Mulford's comments.
Mr Bush and Mr Singh agreed the nuclear deal in 2005
"These remarks raises serious apprehensions regarding the nuclear cooperation deal being negotiated with the US," the CPI(M) said in a statement.
Mr Mulford has said that his comments to the Press Trust Of India had "been taken out of context".
"Iran is a matter where we know India will vote on the basis of its own national interest," he said.
The Press Trust of India is standing by its interview.