WASHINGTON — Two U.S. Navy patrol boats and their crews were seized by the Iranian authorities in the Persian Gulf on Tuesday during what a Tehran news agency alleged was "snooping."
But the Pentagon and the State Department said that one of the boats had experienced mechanical problems while en route from Kuwait to Bahrain on a routine mission. Administration officials said that the military had lost contact with the boats before they strayed into Iranian territorial waters. They said they had received assurances from Iran that the 10 sailors would be returned soon, perhaps on Wednesday.
The semiofficial Fars news agency in Iran said that the boats had illegally traveled more than a mile into Iranian waters near Farsi Island, the site of a major Iranian naval base. It said that members of the Islamic Revolutionary Guards navy had confiscated GPS equipment, which would "prove that the American ships where 'snooping' around in Iranian waters."
The waters where the boats were sailing are a frequent location for intelligence collection by the United States, Iran and many Gulf countries. The U.S. and Iranian navies encounter each other frequently there.
The detention of the sailors comes at a particularly delicate moment in the tense U.S.-Iranian relationship, just days before the formal implementation of a nuclear deal in which the United States is supposed to unfreeze about $100 billion in Iranian assets.
That step is to be made after international nuclear inspectors verify that Iran has shipped 98 percent of its nuclear fuel out of the country and disabled and removed centrifuges, and taken a large plutonium reactor permanently offline.
The U.S. sailors were aboard two riverine patrol boats — 38-foot, high-speed boats that are used to patrol rivers and littoral waters. One official said the two vessels, which often patrol shallow waters near Bahrain, had failed to make a scheduled rendezvous with a larger ship to refuel.
Secretary of State John Kerry, an official said, was notified of the seizing of the sailors while meeting with top Philippines officials and Defense Secretary Ash Carter. Kerry broke off the meeting and called his Iranian counterpart, Mohammad Javad Zarif, with whom he spent months negotiating the nuclear accord. As he walked into the House chamber Tuesday night for President Barack Obama's State of the Union address, Kerry said the sailors were "going to get out."
It is unclear what power Zarif may have to intervene. Many U.S. and Middle Eastern officials believe that recent actions by the Iranian navy against U.S. forces in the Gulf may be intended to embarrass Zarif and President Hassan Rouhani. The Iranian Revolutionary Guards Corps was responsible for the military side of the nuclear program, and many of its senior officers have objected to the nuclear agreement.
U.S. and European officials say that the nuclear accord should go into effect sometime next week. That is called "implementation day," and it is crucial to Rouhani, who wants to demonstrate to voters that he has succeeded in getting oil and financial sanctions lifted, and Iranian funds unfrozen, ahead of a critical parliamentary election.
Many Republicans in Congress have vowed to prevent that day from coming. Obama issued a veto threat on Monday against a House bill that would delay implementation day until the president can certify that Iran has come reported all of its past work toward designing a nuclear weapon. International inspectors recently declared that Iran had a program "consistent" with weapons work through 2009, but that it then ceased. Iran has always denied it ever sought a weapon.
Obama and Rouhani share the same problem: Their political opponents want to kill the deal. Both men are determined to see it through.
The Treasury Department is expected to place some new sanctions on Iran for recent missile tests — which are not covered by the nuclear pact — but that effort has been delayed for reasons U.S. officials will not discuss. A draft of the sanctions declaration was circulated on Capitol Hill just before the new year and quickly leaked.
In the skies and waters of the Persian Gulf, the Strait of Hormuz, the Arabian Sea and the Gulf of Aden, Iran and the United States constantly watch each other. U.S. naval ships roam the waters along Iran's 1,100-mile southern coastline, their radar trained on the shore and on Iranian ships leaving harbors. Iranian fighter jets patrol, keeping an eye on American combat planes that take off from an aircraft carrier in the Persian Gulf every time an Iranian jet comes close to their ship.
The Navy's 5th Fleet maintains a presence in the Persian Gulf, including the aircraft carrier, and lately has had several episodes with Iran. Two weeks ago, the Iranian navy harassed a U.S. carrier and a French frigate in the Strait of Hormuz, launching rockets that passed within 1,500 yards of the aircraft carrier USS Harry S. Truman.
Last year in the Gulf of Aden, an Iranian navy frigate approached a ship where a U.S. military helicopter had just landed and pointed a heavy machine gun at the copter for several minutes before turning around, all while an Iranian film crew videotaped the encounter. The 5th Fleet has its own videotape of the episode.
In 2007, the Revolutionary Guards navy captured 15 British military service members and held them for 13 days, making a point of protecting its sea borders. A year later, the British navy released a report saying that its vessels had been in an area with disputed borders between Iran and Iraq.