FUJAIRAH, United Arab Emirates — A U.S. drone was shot down in international airspace above the Strait of Hormuz on Thursday, U.S. Central Command said, contradicting a claim by Iran’s Revolutionary Guard that it had struck the aircraft after it entered Iranian airspace.

The news comes amid rising tensions in the region, with American officials blaming Iran for what they said was an attack on two oil tankers in the Gulf of Oman last week. Iran has denied any involvement.

A Central Command spokesman, Capt. Bill Urban, said in a statementthat a surface-to-air missile hit an RQ-4A Global Hawk in international airspace above the strait. He called the incident "an unprovoked attack."

Iranian and U.S. officials have previously delivered conflicting reports identifying the drone as an RQ-4A Global Hawk or its naval variant, the MQ-4 Triton.

Iran’s Islamic Revolutionary Guard Corps said in a statement early Thursday that the U.S.-made Global Hawk surveillance drone was brought down by its air force near the Kouh-e Mobarak region, after the aircraft had violated Iranian airspace.

In a later statement, they said the drone left a U.S. base in the Persian Gulf shortly after midnight local time on Thursday, moved around the Strait of Hormuz before entering Iranian airspace four hours later when it was immediately shot down.

The commander of the Revolutionary Guard, Gen. Hossein Salami, said on state television that the strike served as a signal that Iran will not back down from threats. "We have no intention of war, but we are standing strong," he said.

The head of Iran’s national security council said the country’s airspace is its red line, and there would have been a firm response regardless of which country trespassed.

But Urban disputed the allegations, saying, "Iranian reports that the aircraft was over Iran are false."

The incident comes a day afterthe U.S. militarysaid that the one of the tankers sabotaged in the Gulf of Oman last week was attacked with limpet mines that bore "a striking resemblance" to devices in Iran’s arsenal.

Acting Defense Secretary Patrick Shanahan announced Monday that the Trump administration would send 1,000 additional troops to the region.

Shanahan said that the decision to increase forces was a response to a request from Central Command to address air, naval and ground-based threats.

Shanahan stepped down Tuesday and withdrew his name from consideration to be named permanently to the Cabinet position. President Donald Trump named Secretary of the Army Mark Esper, a former Raytheon executive, to take Shanahan's place as acting defense secretary.

That announcement came within minutes of a report published in The Washington Post that outlined a series of alleged domestic violence incidents within Shanahan's family. Shanahan said in a statement that it was "unfortunate" that details from the Post story were "dredged up." He said that continuing with the confirmation process would harm his children. NBC News has not confirmed The Post’s report.

Earlier this week, Central Command said in a statement that a U.S. MQ-9 drone was shot down over Yemen on June 6 by what it thinks was a Houthi SA-6 surface-to-air missile. Iran-allied Houthi rebels are fighting Saudi-backed forces in Yemen in a conflict that has become one of the world's worst humanitarian crises.

“The altitude of the engagement indicated an improvement over previous Houthi capability, which we assess was enabled by Iranian assistance,” Central Command said in the statement about that incident.

Central Command also said this week that on June 13 “a modified Iranian SA-7 surface-to-air missile” attempted to shoot down a different drone of the same type that had arrived to monitor one of the ships damaged in the Gulf of Oman in the incident involving the two tankers.

That missile was ineffective, Central Command said.

“Subsequent analysis indicates that this was a likely attempt to shoot down or otherwise disrupt the MQ-9 surveillance of the IRGC attack on the M/T Kokuka Courageous,” Central Command said of that alleged attempt, referring to the Revolutionary Guard and one of the tankers involved.

Courtney Kube reported from Fujairah, United Arab Emirates, Ali Arouzi from Tehran and Phil Helsel from Los Angeles.