ISTANBUL — The United States, Britain and Israel on Sunday all accused Iran of carrying out a drone attack last week on an oil tanker in the Arabian Sea that killed two people on board, raising fears of an escalating maritime war in the Middle East, as Tehran denied responsibility for the strike.

American and Israeli officials had previously said that Thursday’s attack on the Liberian-flagged Mercer Street bore the hallmarks of an operation by Iran, which has been accused of deploying attack drones in the past. The Mercer Street is managed by Zodiac Maritime, a London-based company owned by an Israeli billionaire. Those killed included a British national and a Romanian citizen, the company said.

Hostilities over the past two years between Israel and Iran have frequently played out at sea, in tit-for-tat attacks by both countries on oil tankers, private commercial vessels or warships — a conflict often referred to as part of a “shadow war” that feels increasingly overt. The strike on the Mercer, off the coast of Oman, marked a significant escalation and was the first time fatalities had resulted from one of the recent attacks.