Two supertankers with Chinese connections abruptly reversed course in the Strait of Hormuz this week, a sign that shipping risks through the vital waterway remain far from settling down. The Sea V, carrying crude oil out of Iraq, was making its way toward Hormuz from the Persian Gulf on Tuesday when it suddenly turned around. Ship-tracking data cited by Bloomberg reportedly shows the vessel is now idling in the middle of the strait. A second tanker, the Hestia, entered the gulf along the Omani coast early Wednesday before also reversing and heading back out. Neither company nor tracking data has offered a clear explanation for why either ship changed course.

Both vessels are very large crude carriers flagged to Hong Kong, and both were broadcasting that they had Chinese crews aboard. A third ship, a fuel tanker called Amara with ties to the United Arab Emirates, made several U-turns of its own in the strait on Tuesday and was still sitting in the waterway near Iran as of Wednesday.

Iran’s lead negotiator with the United States added that the strait will not reopen until Washington meets a specific set of demands. Those include lifting the US naval blockade, removing oil sanctions, and ending military operations in the region.