June 16 (UPI) -- Japan is asking for more evidence from the United States Iran was responsible for attacks against two oil tankers in the Gulf of Oman, including the Kokuka Courageous, a Japanese ship.
The request for proof comes after U.S. Secretary of State Mike Pompeo said Tehran is responsible for the attacks that forced the crew of the ships to be rescued and their cargoes unloaded.
The statements from Pompeo are "not convincing," a Japanese government source said Sunday, according to Kyodo News.
Last week Japanese Prime Minister Shinzo Abe tried to mediate U.S.-Iran relations during a summit with supreme leader Ayatollah Ali Khamenei. The attacks took place while Abe and the Japanese delegation were still in Iran.
Following Pompeo's assessment of the attacks, Japan, through multiple diplomatic channels, said the evaluation "has no backing" and that there was no way to conclude Iran was behind the attacks.
Japanese Foreign Minister Taro Kono also made the same statement during a phone call with Pompeo on Saturday, according to Kyodo.
The Kokuka Courageous and a second tanker, the Norwegian Front Altair, are being checked off the coast of the United Arab Emirates.
"Our crew remains on board the Kokuka Courageous. They are safe and well," ship operator Bernhard Schulte Shipmanagement said Sunday.
Iran has denied involvement in the attacks, and Iranian boats have picked up the crew of the Front Altair.
The Kokuka was on its way to Singapore, loaded with methanol, when it was hit.
Hyundai Dubai, a South Korea-operated cargo ship, initially rescued the crew of the Front Altair on Thursday, according to Pulse, a South Korean news service.