World powers and Iran set the clock ticking on a landmark accord placing limits on the Islamic Republic’s nuclear work in return for access to oil and financial markets.

Sunday’s adoption of the deal means that all sides will have to begin implementing the pledges they made three months ago. For Iran, that means mothballing thousands of centrifuges, eliminating 95 percent of its enriched-uranium stockpile and retrofitting a reactor. The U.S. and Europe will make preparation to lift sanctions, which will only occur once the Iranian measures are in place.

“This is a landmark day for an historic deal,” U.K. Foreign Secretary Phillip Hammond said Sunday in a statement. “This will ensure that a nuclear weapon remains beyond Iran’s reach, thus creating a safer region while opening opportunities for Iran to re-engage with the international community.”

More than two years of negotiations culminated in an agreement of more than 100 pages that was signed on July 14 in Vienna. The accord ran into fierce opposition in the U.S. Congress, where a Republican bid to scuttle the deal failed, and among hard-line members of Iran’s parliament.

Twelve years after Iran was found concealing some of nuclear activities, prompting concern it had weapons ambitions, the deal has been described as a victory of diplomacy over the potential use of force.

‘Meticulous Mechanisms’

“You cannot produce trust in the market,” German Foreign Minister Frank-Walter Steinmeier told a crowd of diplomats on Saturday in Tehran. “The glaring lack of confidence on both sides forced us to elaborate meticulous mechanisms.”

“We consider the agreement as an opening for further diplomatic endeavors,” said Steinmeier, who urged Iran to take on a constructive role in solving the conflict in Syria.

The agreement hasn’t diffused tensions between Iran and the west. From missile tests to support for Syria’s regime and military coordination with Russia, Iran is exerting its power in the volatile region. U.S. allies such as Israel and Saudi Arabia have said the nuclear accord will strengthen Iran even more.

Lifting Sanctions

Sanctions against Iran probably will be lifted within the first three months of 2016, after the International Atomic Energy Agency has confirmed the nation has curtailed its nuclear work, diplomats said last month. Once the restrictions are removed, relief is expected to fuel economic growth by lowering barriers to Iran’s oil exports and ending the isolation of its banks.

Iran has said it will offer about 50 energy projects to investors and plans to boost output by about 2 million barrels a day once the deal is in place. The Persian Gulf nation, with the world’s fourth-largest oil reserves, pumped 2.8 million barrels a day last month, according to data compiled by Bloomberg.

In another sign of progress, IAEA monitors last week ended their 12-year investigation into the possible military dimensions of Iran’s nuclear past. Inspectors now have until Dec. 15 to draft and present a final assessment of their inquiry.

Iran’s nuclear work has been the focus international scrutiny since February 2003, when Iranian officials told inspectors visiting Tehran of their plans to begin enriching uranium on an industrial scale. Subsequent discoveries that Iran had secretly procured nuclear materials and technologies led to years of mistrust. In May 2008 and again in November 2011, the IAEA publicly disclosed its suspicions about Iran’s activities.

Iran has consistently denied ever seeking a nuclear weapon.

Timeline to lifting sanctions:

* Sunday -- “Adoption Day” for July accord signed with world powers. Parties to the agreement begin meeting their commitments.

* Nov. 30 -- Iran prepares to end testing of advanced centrifuge cascades and store machines under IAEA seal.

* Dec. 15 - - IAEA to present its assessment of Iran’s past nuclear activities, which board will use “with a view to closing the issue.”

* Late 2015-early 2016 -- Oil sanctions to be lifted on “Implementation Day.” U.S. officials have suggested it will take at least two months from “Adoption Day” to reach this point.