NEW DELHI, May 4 (Reuters) - Indian MPs from both left and right united on Friday to denounce U.S. legislators for what they said was an attempt to influence foreign policy through a controversial nuclear trade deal.
The lawmakers criticised letters written by Democratic and Republican legislators warning Prime Minister Manmohan Singh that New Delhi's ties with Iran had significant potential to harm India-U.S. relations and the landmark deal.
"We must send a very strong message to the U.S. Senators and Congressmen that this will not prevail," Yashwant Sinha, foreign minister in the previous Hindu nationalist-led government, told parliament.
"We are not going to tolerate this," he said.
The angry reactions from Sinha and his colleagues in the upper house of parliament came after details of the latest letter from the congressmen were published in an Indian newspaper on Friday.
The letter -- signed by Democrat Tom Lantos, chairman of the House of Representatives Foreign Affairs Committee, senior Republican Ileana Ros-Lehtinen and others -- was the third, and strongest, in recent days expressing concern over relations between New Delhi and Tehran.
They urged India to end what they said was "military cooperation" with old friend Iran and terminate participation in the development of Tehran's energy sector.
"I would like to express our very, very strong protest... at what we can only term the temerity of some U.S. senators in insulting our honourable prime minister," said Brinda Karat of the Communist Party of India (Marxist), which shores up the ruling coalition.
The letter was "nothing but an open threat to the sovereignty of this country", she said.
In a separate statement, her party said it had repeatedly pointed out that the nuclear cooperation agreement would seriously damage India's foreign policy and strategic autonomy.
The nuclear deal aims to overturn a three-decade U.S. ban on the sale of nuclear reactors and fuel to New Delhi -- to help meet India's soaring energy needs -- even though it has not signed the nuclear Non-Proliferation Treaty and has tested nuclear weapons.
It is considered the showpiece of a new friendship between the two nations and was approved by the U.S. Congress in December.
But it has run into rough weather over a bilateral agreement that will govern nuclear trade with India saying that the pact included new conditions unacceptable to it.
U.S. legislators and administration officials have in the past also linked the deal to India's stance on what they say is Iran's covert nuclear weapons programme and urged New Delhi to abandon plans to build a gas pipeline from Iran to India.
Officials of the two countries claimed extensive progress over the deal after talks in Washington this week and are due to negotiate again in New Delhi this month.
Indian Parliamentary Affairs Minister Priyaranjan Dasmunsi said the government would continue to remain transparent.
"I would like to make it clear that our government is not in a position to make any kind of compromises that would affect the sovereignty of the country in any way," he told parliament.
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