WASHINGTON – Iran is on track to comply with a landmark arms control agreement even as it squabbles with regional archrival Saudi Arabia, and has tested ballistic missiles in apparent violation of a United Nations resolution.

Barring last-minute problems, Tehran appears likely to fulfill its to-do list and curb its nuclear weapons capabilities this month or next. If it does, the U.N. will be obligated to ease economic sanctions, meaning more than $50 billion in frozen assets and oil revenue will be returned to Iran just as the U.S. presidential primaries are in full swing.

Although the terms of the accord have been public since last summer, the timing of the so-called implementation day seems especially awkward for the White House, which considers the disarmament deal a signature foreign policy achievement for President Barack Obama and is eager to see it succeed.

Critics say the White House is too eager, especially given the uncertain Middle Eastern political landscape on which the deal is playing out.

On Tuesday, skeptics may have gained more ammunition when Iran’s coast guard detained 10 U.S. sailors after their two Navy patrol boats broke down and apparently strayed into Iranian waters. It wasn’t immediately clear whether the Americans were rescued or captured, but the White House said they believed the sailors would be freed promptly.

The incident comes two weeks after the Obama administration notified Congress that it intended to impose new financial sanctions on Tehran for the missile launches, but then abruptly pulled back. Although the White House said sanctions are still planned, the backpedaling has emboldened Iran, lawmakers in both parties have charged.

Some analysts argue that the U.S. vacillation set the stage for a dangerous diplomatic flare-up several days later between Saudi Arabia, a longtime U.S. ally, and Iran, which remains deeply hostile to Washington.

After the Sunni-dominated Saudi government executed a Shiite Muslim cleric who was a prominent political critic, ignoring U.S. pleas to spare his life, Iranian protesters stormed and burned the Saudi Embassy in Tehran while police reportedly stood by.

The Saudi government responded by cutting diplomatic ties with Tehran, and several Saudi allies quickly followed suit. Iran apologized for the embassy attack and sought to downplay its latest diplomatic isolation, partly in hopes that the nuclear deal will help it escape years as a pariah state.

Saudi Arabia is alarmed by what it sees as an ascending Iran, especially as a result of the nuclear deal that they fear will allow the Islamic Republic to simply postpone its nuclear ambitions.

Analysts say Saudi rulers have lost confidence in Washington as an unflinching ally, and they may be seeking to stoke sectarian violence in the region. The kingdom then could claim it is a bulwark against Iranian aggression.

For its part, the Obama administration has taken a neutral stance in the dispute. Secretary of State John F. Kerry spent hours on the phone with his Iranian counterpart and with the Saudi deputy crown prince, urging both sides to “de-escalate,” according to a spokesman.

“Iran sees it has a chance to get out of the penalty box, and they don’t want a fight with Saudi Arabia right now,” said Cliff Kupchan, chairman of the Eurasia Group, a New York-based organization that analyzes international affairs.

U.S. experts say Iran’s leaders still want to see the nuclear deal proceed: President Hassan Rouhani because of the boost it may give moderates in parliamentary elections next month, and supreme leader Ali Khamenei because it allows Iran to re-enter the global marketplace and inject life, and cash, into its moribund economy.

The Obama administration also wants Iran to meet its obligations, stressing that the turmoil in the Middle East will grow far worse if Iran were to obtain a nuclear bomb.

While recognizing severe differences between Shiites and Sunnis, the administration wants to focus on the nuclear deal, negotiations aimed at ending the civil war in Syria, efforts to combat Islamic State militants and “issues affecting the Middle East writ large,” according to John Kirby, a State Department spokesman.

Iran has given mixed signals about its intentions.

In addition to complying with the nuclear deal, it has not pulled out of the U.N.-backed Syria talks, which are due to start Jan. 25, and is supporting Iraqi government troops in some combat operations against Islamic State.

In Iran, the months after the deal was signed in July saw an uptick in anti-U.S. rhetoric and crackdowns on dissidents. Those actions may have been a sop to domestic hard-liners who oppose any rapprochement with the West.

But Tehran also conducted several ballistic missile tests, including one in October that the U.S. considers a violation of a U.N. resolution and another similar test in November. Last month, a smaller Iranian rocket reportedly came within 1,500 feet of a U.S. aircraft carrier in the Strait of Hormuz.

Even some Democrats, including Rep. Debbie Wasserman Schultz, D-Fla., the party chairwoman, denounced the White House for not penalizing Tehran for the missile launches.

“The United States and our allies must take immediate, punitive action and send a clear message to Iran that violating international laws, treaties and agreements will have serious consequences,” Schultz and six other House Democrats wrote in a letter this month to Obama.

“Inaction . would send the misguided message that, in the wake of the (nuclear deal), the international community has lost the willingness to hold the Iranian regime accountable for its support for terrorism and other offensive actions throughout the region,” they wrote.

Iran is “testing the limits of international patience” with its missile launches, said Ray Takeyh, a senior fellow with the Council of Foreign Relations and former adviser to the Obama administration.

“Since the advent of the (nuclear) deal in July, Iran has become more aggressive in the region, more repressive at home and less compliant with its arms control obligations,” Takeyh said. “But in terms of the actual components of the accord, I think the accord was very favorable to Iran. It would be in their interest to sustain it.”

Iran already has made significant moves to comply with the nuclear deal.

Last month, Iran shipped 12.5 tons of enriched uranium to Russia, nearly its entire stockpile, as required by the agreement. Losing that potential bomb fuel triples the time Iran would need to produce a nuclear weapon, U.S. officials say, a key goal of the six world powers that negotiated the deal last summer in Vienna.

Next, Iran must dismantle or mothball thousands of centrifuges, which are used to enrich uranium, and pour concrete into a heavy water reactor before it can produce any plutonium, another potential bomb fuel.

Once the International Atomic Energy Agency, the U.N.’s nuclear watchdog agency, certifies that Iran has met its obligations, the Security Council can vote to lift U.N. sanctions. The five permanent members of the Security Council plus Germany negotiated the deal with Iran.

Various countries or country blocs then can begin to ease sanctions and release billions of dollars in Iranian funds frozen in banks and financial institutions.

It is likely that the first money to become accessible to Iran is an estimated $50 billion to $60 billion from exports of Iranian oil to several Asian countries. The money has been sitting in Asian banks for years.

The U.S. embargo on trade with Iran will continue, but several exceptions will be allowed, including the import and export of foodstuffs.

Iranian individuals will be removed from U.S. government blacklists, while Europe will allow trade in software, gold and metals, and transportation equipment. Iran will be allowed to rejoin the international banking system and will be permitted to resume selling oil and other energy supplies on the open market.