FUJAIRAH, United Arab Emirates -- The hijackers who captured a vessel off the coast of the United Arab Emirates in the Gulf of Oman departed the targeted ship Wednesday, the British navy reported, as recorded radio traffic appeared to reveal a crew member onboard saying Iranian gunmen had stormed the asphalt tanker.
The incident -- described by the British military's United Kingdom Maritime Trade Operations the night before as a "potential hijack" -- revived fears of an escalation in Mideast waters and ended with as much mystery as it began.
Hints of what unfolded on the Panama-flagged asphalt tanker, called Asphalt Princess, began to emerge with the maritime radio recording, obtained by commodities pricing firm Argus Media. In the audio, a crew member can be heard telling the United Arab Emirates coast guard that five or six armed Iranians had boarded the tanker.
"Iranian people are onboard with ammunition," the crew member says. "We are ... now, drifting. We cannot tell you exact our ETA to [get to] Sohar," the port in Oman listed on the vessel's tracker as its destination. It was not clear whether the crew members, whom he identified as Indian and Indonesian, were in immediate danger.
No one took responsibility for the brief seizure, which underscored mounting tensions as Iran and the U.S. seek a resolution to their standoff over Tehran's tattered 2015 nuclear deal with world powers.
Apparently responding to the incident, Iranian Foreign Ministry spokesman Saeed Khatibzadeh on Tuesday denied that Iran played any role. He described the recent maritime attacks in the Persian Gulf as "completely suspicious."
Over the past years, the rising tensions have played out in the waters of the Persian Gulf, where just last week a drone attack off the coast of Oman on an oil tanker linked to an Israeli billionaire killed two crew members.
The West blamed Iran for the raid, which marked the first known fatal assault in the yearslong shadow war targeting vessels in Mideast waters. Iran denied involvement.
Late Tuesday, the intruders boarded the Asphalt Princess sailing off the coast of Fujairah, authorities said. The official news agency of Oman's military said it received reports that the Asphalt Princess had been hijacked and immediately dispatched its maritime patrol aircraft and naval vessels "to contribute to securing international waters."
In the recorded radio traffic, when the UAE coast guard asks the crew member what the Iranian gunmen were doing onboard, he says he "cannot understand the [Iranians]," his voice muffled, before trying to hand over the radio to someone else.
The call then cuts off.
Possible signs of trouble began to emerge that evening when six oil tankers off the coast of Fujairah announced around the same time on their Automatic Identification System trackers that they were "not under command," according to MarineTraffic.com. That typically means a vessel has lost power and can no longer steer.
Satellite-tracking data for the Asphalt Princess had showed it gradually heading toward Iranian waters off the port of Jask early Wednesday, according to MarineTraffic.com.
Hours later, however, it stopped and changed course toward Oman, just before the British navy group declared the hijackers had departed and the vessel was now "safe."
In an analysis, maritime intelligence firm Dryad Global described the seizure of the Asphalt Princess as the latest Iranian response to outside pressures, economic conflicts and other grievances.
"Iran has consistently shown that in conducting this kind of operation, it is calculated in doing so, both by targeting vessels directly connected with ongoing disputes and [vessels] operating within the 'grey space' of legitimacy," which may be involved in illicit trade, Dryad Global said.
The owner of the Asphalt Princess, listed as Glory International, could not immediately be reached for comment.