The Strait of Hormuz, the slender waterway that connects the Persian Gulf to the rest of the world and is a critical conduit in the global oil supply chain, has again become a point of contention for Iran and the United States � just as they are trying to reach a nuclear accord.

Responding to Iran�s seizure at gunpoint of a cargo ship that was traversing the strait this week, the United States Navy on Thursday began deploying about a dozen warships there to protect American vessels from possible seizure or harassment. The seized vessel was owned by the Danish company Maersk and registered in the Marshall Islands.

The American decision was seen as a signal to Iran, which historically has regarded the strait, an international waterway, as part of its sphere of influence. Iranian and United States forces battled in the strait 27 years ago. More recently, Iranian gunboats operated by the Revolutionary Guard have harassed foreign shipping in the strait in the name of national security. Iran�s military has also used the area as a backdrop for propaganda.

What is different this time is that both Iran and the United States are engaged in the final weeks of multilateral talks on an agreement that could resolve the longstanding dispute over Iranian nuclear activities. The deadline for reaching that agreement is June 30.

Such an achievement, which President Obama and President Hassan Rouhani of Iran have signaled they clearly want, could portend the end of Iran�s economic isolation and possibly lead to a reconciliation of an estranged relationship that has helped define Middle Eastern politics for four decades.

While it is unclear whether a new showdown between Iran and the United States on the strait could jeopardize the nuclear talks, the fear is that an accidental or inadvertent confrontation could escalate.

�The real if low probability threat to the talks arises from possible miscalculation,� Cliff Kupchan, chairman of the Eurasia Group, a political risk consultancy in Washington and its expert on Iran, said Friday.

�As in previous tense periods, there will now be a lot of U.S. and Iranian military assets in proximity near the strait,� Mr. Kupchan said. �Both sides� personnel will be tense. A mistake could change the game.�

The strait, 21 miles wide at its narrowest point, is the conduit for about 40 percent of the world�s oil tanker traffic. It falls within territory claimed not only by Iran but by Oman and the United Arab Emirates.

Despite Iran�s threats in the past to completely close the strait during times of acute tensions, it has never done so, although military analysts have said the Iranians could lay mines across the waterway within a matter of days, paralyzing traffic.

Iranian officials, including Foreign Minister Mohammad Javad Zarif, have said in recent days that Iran has no intention of obstructing or stopping traffic in the strait.

Nonetheless, Iran is expected to respond to the Navy�s increased presence in the area.

Under international maritime law, ships of all nations may traverse the strait. They are obliged to follow special navigation rules known as the Traffic Separation Scheme. An inbound lane and outbound lane, each one mile wide, is separated by a two-mile buffer zone on either side.

The lanes leave little room for maneuvering enormous oil tankers and other large vessels, and the additional deployment of military ships could make the lanes more crowded � creating more potential for accidents.

The strait has been the backdrop of military bluster and confrontation between Iran and other nations since the 1979 Islamic Revolution. In 1984 Iran threatened to close the strait after Iraq attacked Iranian shipping during the Iran-Iraq War.

American and Iranian forces clashed there repeatedly in 1988 after a Navy frigate was damaged by an Iranian mine. On April 18 of that year, American forces sank three Iranian warships and destroyed two surveillance platforms in what was known as Operation Praying Mantis.

�People don�t remember we fought a miniwar with Iran in an afternoon,� said Eugene Gholz, a professor of public affairs at the University of Texas who directed a 2008 research study of the Strait of Hormuz and its strategic significance.

On July 3, 1988, an American warship patrolling the strait, the U.S.S. Vincennes, shot down an Iranian commercial airliner, killing 290 people. The ship�s crew apparently mistook the plane for an Iranian F-14 fighter.

Iran altered its naval strategy in the strait regarding the Americans after the confrontations in 1988, shifting to the use of smaller nimble speedboats that could outrun the more powerful warships of the United States Fifth Fleet, which is based in Bahrain.

There is a widespread view that Iran has no desire to let the latest tensions with the United States in the strait get out of control. At the same time, analysts said, Iran wants to show � at least to a domestic audience � that its forces will not be bullied.

�They look largely for razzle-dazzle that doesn�t have a big military effect,� Mr. Gholz said. �It would be an accidental escalation. The Iranians don�t want to fight with us. They�ve shown restraint with respect to the U.S. military.�

This article was written by Rick Gladstone for The New York Times on May 1, 2015. He is Reporter and editor on The New York Times Foreign Desk.