The drone hit a vessel in the Egyptian port of Damietta on Wednesday, causing a fire that spread to another vessel, three trading sources familiar with the incident said.
The crew were evacuated and the fire had been brought under control, Ambrey said.
There was no immediate claim of responsibility for the incident.
Earlier on Wednesday the United States and Saudi Arabia struck Iran-backed paramilitary groups in Iraq, and US President Donald Trump vowed to "beat the f***ing shit" out of Iran for firing on US troops days after he halted air strikes.
Iran confirmed overnight that it had fired on US bases in Jordan and at ships in the Strait of Hormuz, and also spurned an Omani proposal to jointly manage the strait.
"We'll be hitting them hard," Fox News quoted Trump as saying.
"We're going to beat the f***ing shit out of them."
Oil prices shot up Wednesday in one of the sharpest spikes of the five-month war. Brent crude futures rose more than eight per cent to push the benchmark well above $US90 ($A130) a barrel, reversing much of a plunge earlier this week when Trump had unexpectedly halted US strikes over the weekend.
The abrupt resumption of attacks only days after they were suspended saw a return to the volatile on-again-off-again pattern of earlier phases in the war.
Trump had said "Operation Epic Fury" would last only a few weeks when he launched it in February but fighting has now gone on for five months with no end sight.
The joint US-Saudi attacks also mark the first time Riyadh has publicly joined strikes alongside Washington. That could widen the conflict by drawing Sunni Muslim Saudi Arabia into combat against Shi'ite proxies of Iran on a new front.
Iraq's Popular Mobilisation Forces, powerful Iran-backed paramilitary groups incorporated into the Iraqi security forces, said at least 20 members were killed and 32 wounded in US-Saudi strikes targeting several bases across Iraq.
Iraqi men shouted Shi'ite sectarian slogans and "Death to America!" as they carried the bodies of slain fighters in body bags out of a hospital in Mosul in northern Iraq, footage from Iraq's Al-Ahad television showed.
Washington and Riyadh said they struck the Iran-backed armed groups in Iraq in retaliation for drone attacks on Saudi oil targets launched from Iraq.
It was the first major US military action in the Middle East since last Friday, when Trump abruptly suspended an intensive bombing campaign after 13 days, having been advised by commanders that the strategy had run its course.
The strikes on Iraq expose a dangerous rift in that volatile country. The Shi'ite-led government is one of the few in the world to balance close military and diplomatic ties with both Tehran and Washington, but those divided loyalties are a constant source of tension and frequent domestic unrest.
The office of Prime Minister Ali al-Zaidi, who took power just two months ago, urged the parties involved to avoid escalation and said he wanted to keep the country out of regional conflicts.
Hours before launching the joint attacks with Saudi Arabia on Iraq, the US military said its air defences had averted a surprise Iranian attack on US troops in the region.
Jordan's military said it had shot down five Iranian missiles. US bases in Jordan have lately become primary Iranian targets, where three US service members were killed this month in the worst US losses since March.
Iran's Revolutionary Guards said they had fired several ballistic missiles at US military installations in Jordan, and had struck three tankers that were attempting to transit through the Strait of Hormuz along an unauthorised route.
