Fresh attacks Tuesday (May 14) on oil supplies in the Middle East.
Just days after these tankers were hit at anchor off the UAE, Saudi Arabia says a pipeline and pumping station near Riyadh have been struck by armed drones.
Earlier Tuesday, a Houthi-run TV station said the Yemeni group had carried out drone attacks on Saudi assets.
It wasn't clear if that was a claim of responsibility for the tanker or pipeline incidents.
Reuters oil correspondent Dmitry Zhdannikov is following the story from London.
SOUNDBITE (English) REUTERS OIL CORRESPONDENT, DMITRY ZHDANNIKOV, SAYING: "There haven't been any convincing statements from either side to say, to blame anyone, for instance I mean people have suggested it could be Iran but there have been no statements from either the Saudi or American side and Iran has actually denied having anything to do with the attacks and said it's very 'worrisome'".
On Tuesday one Iranian lawmaker called the tanker attacks 'Israeli mischief'.
U.S. officials said such statements were an attempt to muddy the waters.
Washington's ambassador to Saudi Arabia called for "reasonable responses short of war" - once the culprits are identified.
The U.S. has sent aircraft carriers and bombers to the region amid its escalating dispute with Iran over the country's nuclear programme.
Some fear the tanker attacks could prove the flashpoint for conflict.
Oil held steady after the tanker attacks, but then jumped following the news of the pipeline bombing.
International benchmark Brent crude rose as much as 1.4 percent Tuesday.
Any conflict in the region would be likely to see prices jump even more sharply.
Around a fifth of the world's oil passes through these waters, making any threat to tankers a global concern.