Iran will get a first installment around February 1 of $550 million of $4.2 billion being unblocked under a six-month landmark nuclear deal with the West, a US official said Sunday.

"The installment schedule starts on Feb. 1 and the payments are evenly distributed" across 180 days, a senior US administration official told AFP.

"That means the installment payments are every 34 days, except the last payment happens on day 180, which is 33 days after the 5th installment payment," the official said in an email, asking not to be named.

However, as February 1 is a Saturday, the first payment might not be made until February 3.

The money is being unblocked under a landmark deal, set to take effect starting January 20, that curbs parts of Iran's disputed nuclear program in exchange for sanctions relief.

Tehran agreed in November to roll back parts of its nuclear work and halt further advances in exchange for the release of $4.2 billion in frozen assets and limited relief from sanctions that have choked its hard-hit economy.

There will be a second installment on March 7 of $550 million, followed by equal installments of $550 million monthly with the last due on July 20, although that again is a Saturday and therefore could take place on July 21.

In addition, a payment of $450 million is planned for March 1 in return for Iran diluting half its stock of 20 percent enriched uranium to no more than 5 percent.

A second similar payment of $450 million will be due on April 15 if Tehran completes the dilution of all its stock of 20 percent enriched uranium.

Under this schedule, Iran will receive two injections of cash in both March and April if, as agreed, it waters down its 20 percent enriched uranium, ensuring it will no longer be weapons-grade material.

Main points in the Iran nuclear deal
Tehran Jan 12, 2014 - Iran said on Sunday that an accord it struck with world powers on its disputed nuclear programme in exchange for an easing of sanctions will take effect from January 20. The United States confirmed the news although President Barack Obama warned of a tough road ahead to real a comprehensive solution. Following are the main points in the interim nuclear deal signed between Iran and the P5+1 -- Britain, China, France, Russia and the United States, plus Germany -- on November 24. Under the deal Iran agreed to curb parts of its nuclear drive for six months while a "comprehensive solution" is negotiated, in exchange for modest relief from international sanctions and a promise by world powers not to impose new measures against its hard-hit economy. The sanctions have been imposed to pressure Iran into halting what Western countries fear is a plan to develop a nuclear arsenal and tip the balance of power in the Middle East. Iran maintains its nuclear drive is for peaceful purposes only. Main points * Iran has agreed it will not enrich uranium over five percent for the six months. * Iran has committed to neutralising its entire stockpile of uranium enriched to 20 percent, which is close to weapons-grade and therefore a main area of concern. Half of this will be diluted to five percent or under. The rest will be oxidised so it can contribute to making fuel for a Tehran reactor that produces medical isotopes. * Iran will build no new locations for enrichment, and halt progress towards commissioning a reactor at its Arak plant that would produce plutonium that could also be used in a nuclear bomb. * Iran will not reprocess or construct a facility capable of reprocessing spent fuel from the Arak reactor in order to extract plutonium. * Iran will allow daily site inspections by experts from the UN nuclear watchdog IAEA at two of its enrichment facilities -- Fordo and Natanz -- and hand over information about the design of its Arak reactor. * The P5+1 powers and Iran will establish a "joint commission" to work with the International Atomic Energy Agency and monitor implementation of the agreement. * In return, the P5+1 will ease sanctions in what the White House has described as a "limited, temporary, targeted, and reversible" manner to the tune of about $7 billion, but the "vast bulk" of oil, finance and banking sanctions will remain in place. * The UN Security Council and European Union will not impose any new nuclear-related sanctions for six months. * They will suspend US and EU sanctions on Iran's petrochemical exports and associated services such as insurance or transportation, and on gold and precious metals and associated services. They will also suspend US trade restrictions on Iran's auto industry and associated services and licence the supply and installation in Iran of spare parts for flight safety. * An agreed amount of revenue from sanctioned Iranian oil sales held abroad will be repatriated.