A group of 83 U.S. senators and 395 members of the House have sent two joint letters from their respective bodies to President Barack Obama, urging him to take a hard line on Iran in the final agreement on its nuclear capacity.

The first letter delivered to the president came from the senators: Topping their list of "core principles" they hope will guide the final agreement is the admonishment that Iran "has no inherent right to enrichment," in keeping with the Nuclear Non-Proliferation Treaty.

Second on the list of the 83, led by Robert Menendez, is to ensure that the final agreement prevents Iran from ever having the means to build a nuclear bomb.

While complimenting the president on his actions to constrain Iranian nuclear development, the senators also urge Obama to maintain economic sanctions which "brought Iran to the table" until Tehran abandons its ambition to build nuclear weapons – for all time.

Under the circumstances, Iran has "no reason to have an enrichment facility like Fordow," write the senators. Tehran should also get rid of its heavy-water reactor at Arak, which by the way Iran admitted this week was sabotaged.

To make sure Iran complies with the conditions of this wishful final agreement, the senators say Iran must submit to "long-term and intrusive" inspections.

Throughout the letter, the senators seem to feel the need to remind Obama of Congress' role in forming the American response to Iran's actions. Having repeated that yet again, the letter closes with the thought: What to do if Iran rejects the final agreement? Impose "much more dramatic sanctions," the senators prescribe, including curbs on its export of oil.

The members of House sent a similar letter hours after, demanding "stringent transparency measures to guarantee that Iran cannot develop an undetectable nuclear weapons breakout capability."

"None of us desires military conflict," wrote the representative, "but as you

yourself have acknowledged, we must keep all options on the table to prevent this

dangerous regime from acquiring nuclear weapons. The first signatory on the letter belonged to House Majority Leade Eric Cantor."

Sparring ahead of talks

Israel has also been adamant that Iran must be prevented from developing nuclear arms. One aspect of the local debate has been whether Israel should attack Iran's nuclear facilities on its own, or wait for America to make a move. On Monday, Israeli Defense Minister Moshe Ya'alon intimated that he had changed his mind and now thought Israel should go it alone, if needed, not wait for the "weak" U.S.

In November, Iran and the G6 struck an interim deal. According to it, Tehran has since shelved higher-grade uranium enrichment - a potential path to atomic bombs - and obtained modest relief from punitive economic sanctions in return.

Talks towards a final agreement commenced today in Vienna. Western officials are concerned the negotiations will be muddied by the Ukraine problem: The West and Russia find themselves at loggerheads over the future of that country, which could hamper agreement over Iran.

Meanwhile, European Union foreign policy chief Catherine Ashton is leading the negotiations on behalf of the powers – but Iranian Foreign Minister Mohammad Javad Zarif had canceled a customary pre-talks dinner with Ashton on Monday evening. The official IRNA news agency quoted sources as saying it was because of Ashton's "undiplomatic" behavior, an apparent reference to her meeting Iranian human rights activists during her first visit to Tehran 10 days ago.

Open gallery view The suspected uranium-enrichment facility of Fordow near Qom, 156 km southwest of Tehran, seen in this September 27, 2009 satellite photograph released by DigitalGlobe on September 28, 2009. Credit: Reuters