A group of US Republican senators has written an open letter to Iran’s leaders, suggesting that any decision based on nuclear negotiations with the current government and signed by President Obama can be revoked after he leaves office in early 2017.

"We will consider any agreement regarding your nuclear-weapons program that is not approved by the Congress as nothing more than an executive agreement between President Obama and Ayatollah Khamenei," says the senators' letter to the leaders of the Islamic Republic of Iran, as reported by Bloomberg.

Vice-President Joe Biden denounced the letter from GOP senators in strongest terms, saying than in 36 years in the US Senate he “cannot recall another instance in which senators wrote directly to advise another country — much less a longtime foreign adversary — that the president does not have the constitutional authority to reach a meaningful understanding with them.

"The decision to undercut our president and circumvent our constitutional system offends me as a matter of principle,” Biden added.

Iran's Minister of Foreign Affairs Javad Zarif dismissed the GOP letter as a "propaganda ploy," saying that while negotiations are still going on, “some political pressure groups are so afraid even of the prospect of an agreement that they resort to unconventional methods, unprecedented in diplomatic history.”

READ MORE: US hammers out ‘bottom lines’ for Iran nuclear deal

Signed by the entire Republican party leadership, including several potential 2016 primaries' presidential runners, the document warned Iran's government that an agreement signed by Obama may not last for long, as it could be revoked by the next president "with the stroke of a pen."

Referring to the US Constitution, almost 50 politicians said that while it is the president who negotiates international agreements, "Congress plays the significant role of ratifying them."

The senators explained their move to be educational, aiming to "enrich your [Iranian leaders] knowledge of our [US] constitutional system." They pointed out: "Obama will leave office in January 2017, while most of us will remain in office well beyond then - perhaps decades," they wrote, referring to a constitutional right of senators' unlimited number of 6-year terms.

Well, that's embarrassing. "US civics education" letter to Iran from 47 GOP senators gets treaty ratification wrong. http://t.co/9OEi3lE89O — Yishai Schwartz (@YishaiSchwartz) March 9, 2015

Warning Iran to "seriously consider" their letter "as negotiations progress," the initiative can also be regarded as Congress's effort to obtain more authority from the White House in the talks and decision making over the nuclear deal. Tensions over the negotiation process have already increased within the US, especially after last week's controversial visit by Israeli Prime Minister Benjamin Netanyahu.

Senate calls for more of a role in US-Iran nuke negotiations: http://t.co/ItA5KP00dvpic.twitter.com/33svNwEtiY — The Hill (@thehill) February 28, 2015

Netanyahu’s invitation to speak before Congress was extended to the Israeli leader by Republican lawmakers without the prior knowledge of the White House, which is standard protocol in such cases. After the speech, Obama said Netanyahu did not offer any real alternative amid the ongoing negotiations, while the Israeli leader has called his trip to Washington "a fateful, even historic mission."

READ MORE: Netanyahu offered no ‘viable alternative’ to Iran nuclear deal - Obama

The ongoing talks on Iran's nuclear ambitions and uranium enrichment capacity, with the so-called P5+1 group (the US, Britain, China, Russia, France and Germany), failed to reach a conclusion by the previous deadline of November last year. Now negotiators are under pressure to reach an agreement with Iran by the end of this month, with the final technical details to be hammered out by June 30.