WASHINGTON - A US aircraft carrier sailed through the Strait of Hormuz and into the Gulf without incident on Sunday, a day after Iran backed away from an earlier threat to take action if an American carrier returned to the strategic waterway.

The Nimitz-class aircraft carriers USS John C. Stennis (R) and USS Abraham Lincoln transit during a turnover of responsibility in the Arabian Sea in this U.S. Navy handout photo dated January 19, 2012. The USS Abraham Lincoln sailed through the Strait of Hormuz and into the Gulf without incident on Sunday, a day after Iran backed away from an earlier threat to take action if an American carrier returned to the strategic waterway. [Photo/Agencies]

The carrier USS Abraham Lincoln completed a "regular and routine" passage through the strait, a critical gateway for the region's oil exports, "as previously scheduled and without incident," said Lieutenant Rebecca Rebarich, a spokeswoman for the US Fifth Fleet.

The Lincoln, accompanied by strike group of warships, was the first US aircraft carrier to enter the Gulf since late December and was on a routine rotation to replace the outgoing USS John C. Stennis.  

The departure of the Stennis prompted Iranian army chief Ataollah Salehi to threaten action if the carrier passed back into the Gulf.

"I recommend and emphasize to the American carrier not to return to the Persian Gulf. ... We are not in the habit of warning more than once," he said.

The threat led to a round of escalating rhetoric between the two sides that spooked oil markets and raised the specter of a military confrontation between Iran and the United States.

Iran threatened to close the strait, the world's most important oil shipping gateway, while the United States warned such a move would require a response by Washington, which routinely patrols international sea lanes to ensure they remain open.

Iran appeared to ease away from its earlier warnings on Saturday, with Revolutionary Guard Corps Deputy Commander Hossein Salami telling the official IRNA news agency that the return of US warships to the Gulf was routine and not an increase in its permanent presence in the region.

"US warships and military forces have been in the Persian Gulf and the Middle East region for many years and their decision in relation to the dispatch of a new warship is not a new issue and it should be interpreted as part of their permanent presence," Salami said.

Pentagon officials declined to comment directly on Salami's remarks, but reiterated that continued US presence in the region reflected the seriousness with which Washington takes its security commitments to partner nations in the region and to ensuring free flow of international commerce.  

The Lincoln's arrival in the Gulf was unrelated to Iran's statement on Saturday.

Tensions between Iran and the United States have been escalating in recent weeks as President Barack Obama prepares to implement new US sanctions against Iran over its nuclear enrichment program, which Tehran says is for energy production but the West believes is aimed at producing atomic weapons.

The EU is preparing to intensify sanctions against Tehran with an embargo on Iran's oil exports and possibly freezing the assets of Iran's central bank. Obama is preparing new US sanctions that target foreign financial institutions that do business with Iran's central bank.

Both sides tried to scale down the rhetoric last week. The White House emphasized the United States was still open to international talks on Iran's nuclear program, even as it denied Iranian assertions that discussions were under way about resuming a dialogue.

The White House would not confirm or deny Iranian reports that Obama had sent a letter to Iranian leaders, but spokesman Jay Carney said any communications with Tehran would have reinforced the statements Washington has made publicly.

The United States supports talks between Iran and the so-called P5 + 1, the five permanent members of the U.N. Security Council  - Russia, China, France, England and the United States - plus Germany.

Carney urged Iran to respond to the letter sent in October on behalf of the P5 +1 by European Union foreign policy chief Catherine Ashton.

"If the Iranians are serious about restarting talks, then they need to respond to that letter," Carney told a White House briefing. "That is the channel by which ... the restarting of those talks would take place."