(CNSNews.com) - Left-wing lawmakers in India who oppose a planned nuclear energy cooperation agreement with the United States are up in arms over Washington's advice on how New Delhi should deal with Iran.

Earlier this week, a State Department spokesman appealed for the Indian government to press President Mahmoud Ahmadinejad on the international community's unresolved nuclear dispute with Tehran when the Iranian leader visits next week.

Spokesman Tom Casey said the U.S. hoped India would urge Ahmadinejad to comply with Security Council requirements regarding the nuclear program, including the suspension of uranium enrichment.

Opponents of the Indo-U.S. nuclear deal, including leftist parties whose support in parliament is crucial for the survival of Prime Minister Manmohan Singh's government, seized on the comment, saying it was further proof of U.S. interference in India's affairs.

The Bush administration's proposal to resume civilian nuclear cooperation -- frozen since India began experimenting with nuclear weapons in the 1970s -- is a key element in its strategy, outlined in 2005, to help energy-hungry India become "a major world power" in the 21st century.

The agreement was signed two years ago, but it remains bogged down because the Indian leftists have threatened to withdraw their support for the government if it goes ahead. The State Department warned earlier this month that time was running out if the current U.S. Congress was to have the opportunity to consider the landmark deal for ratification, although the department said it could also be taken up by the next administration and Congress.

Leftists led by the Communist Party of India-Marxist (CPI-M) have long suspected that in exchange for the deal, the U.S. expects India to toe the line on other issues, including support for the West in the dispute with Iran.

Although both the Indian and U.S. governments have denied that there is any linkage between the two issues, skeptical U.S. lawmakers have long argued that India should support the U.S. on Iran if it wishes the deal to go ahead.

When India twice sided against Iran in votes calling for the U.N.'s nuclear watchdog, the International Atomic Energy Agency (IAEA), to refer Tehran to the Security Council, the left-wingers said this was proof that the government was bending to pressure from the U.S.

They were similarly unhappy when the U.S. spoke out against India's plans for a pipeline to bring natural gas from Iran to India, via Pakistan (India, which is anxious to find energy suppliers to fuel its growing economy, dismissed U.S. objections; negotiations on the multi-billion-dollar project continue, but have run into difficulties including a dispute over transit fees Pakistan wants to charge.)

Casey's remark ahead of Ahmadinejad's first visit to India drew an unusually strong response from India's external affairs ministry, which said India and Iran were ancient civilizations which did not need any outside guidance on how to conduct bilateral relations.

The ministry's stance did not satisfy the CPI-M, however, and its lawmakers demanded that the government summon the American ambassador to protest against the "gross interference" in India's relations with other countries.

Accusing the U.S. of "imperialist arrogance," communist lawmaker Brinda Karat said the incident "clearly proves that the U.S. considers India its junior partner."

External Affairs Minister Pranab Mukherjee on Wednesday advised the U.S. to leave the issue of Iran's nuclear programs to the IAEA.

"We tell the U.S., do not take on yourself the responsibility [of determining] whether Iran was manufacturing weapons or not," he told reporters. "Leave it to the IAEA, the designated authority."

Iranian Ambassador to India Mahdi Nabizadeh said Wednesday that neither Tehran nor Delhi would allow Washington's "interference" to affect increasingly close bilateral ties, the official IRNA news agency reported.

Tehran hid its nuclear program for almost two decades before dissidents exposed it in 2002. While the U.S. and allies suspect it is being developed for military purposes, Iran says it wants the technology solely to generate energy supplies.

Despite three Security Council resolutions and sanctions, Iran continues to defy demands to suspend uranium enrichment, and on April 8 announced plans to expand the activities by tripling the number of centrifuges it has operating.

Centrifuges are pieces of equipment that spin at high speeds, enriching uranium to varying degrees, providing fuel for nuclear reactors or, in the case of very high levels of enrichment, a key ingredient for an atomic bomb.

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