The U.S. military said Tuesday that it has canceled a planned port visit in Croatia for a Navy aircraft carrier as its deployment to the Middle East has been be expedited in response to “recent and clear indications” that Iran was preparing to attack U.S. troops in the region.

The USS Abraham Lincoln, traveling with a fleet of escort ships, will make way for the Middle East as part of a deployment announced Sunday by White House national security adviser John Bolton. The Lincoln already was due to “spend a significant amount of time” in the Middle East, but it will now arrive earlier than initially planned, the Pentagon said in an emailed statement responding to questions from numerous reporters.

The Navy announced last month that the carrier and its associated escort ships had deployed from Norfolk.

The expedited deployments also include the Air Force sending B-52s to the Middle East. Bolton’s statement Sunday said a “bomber task force” would deploy but did not specify which planes would be involved. Bombers have regularly rotated through the Middle East for years.

Deployments are typically announced by the Defense Department, and the release of Bolton’s statement Sunday night seemingly caught parts of the Pentagon off-guard. The Defense Department did not release any statement of its own until Monday afternoon, and it did not respond to many follow-up questions until Tuesday afternoon. It has so far declined to hold a news conference on the issue.

Navy Capt. Bill Urban, a U.S. military spokesman, in the response to questions released by the Pentagon on Tuesday said Marine Gen. Kenneth McKenzie, the chief of U.S. Central Command, requested additional forces in the Middle East “to protect U.S. forces and interests in the region and to deter any aggression” after receiving information about a credible threat.

“A number of factors define credibility but they are all related to the sources and methods through which information is obtained, which is not something we are going to be able to talk about,” Urban said.

The Lincoln, which was still more than 1,000 miles away from the Persian Gulf on Saturday, will be positioned in the Middle East by Vice Adm. James Malloy, who commands naval forces in the Middle East. The Pentagon declined to be more specific, citing operational security.

Urban said that the United States continues to closely monitor the actions of Iran, its military and its proxies, and “we are well postured to defend U.S. forces and interests.” The deployment of the Lincoln strike group and the B-52s “are considered prudent steps to protect U.S. forces and interests in the region and to deter any aggression,” he said.

The expedited deployment was approved by acting defense secretary Patrick M. Shanahan on Sunday, following the request by McKenzie, the Pentagon said. Shanahan said in tweets Monday that the moves marked a “prudent repositioning of assets in response to indications of a credible threat by Iranian regime forces."