Two cruise ships passed through the Strait of Hormuz over the weekend during a brief window when the waterway was open to ship traffic, according to the vessels’ German operator.

The two ships, Mein Schiff 4 and Mein Schiff 5, both staffed with skeleton crews and no passengers, “successfully” left the region, the travel operator, TUI Cruises, said. In a statement on Sunday, the company said that the ships had been stranded in the Persian Gulf in recent weeks, as Iran restricted traffic through the strait in response to U.S. and Israeli attacks.

“The passage took place based on the relevant coordination and approvals from the authorities, in a controlled manner and with careful consideration of the security situation,” the statement said. TUI Cruises, which is based in Hamburg, did not respond to a request for details of how the ships had secured safe passage.

The two ships were heading toward Cape Town, South Africa, where they would return to their regular schedules, the company said. The Mein Schiff 4’s voyage from Trieste, Italy, departing May 17, and the Mein Schiff 5’s voyage from Iraklion, Greece, departing May 15, both of which had been canceled, would instead go ahead as planned, and passengers’ bookings automatically reactivated, the travel operator said.

The ships are among the small number that managed to cross the Strait of Hormuz over the weekend during the brief period when the Iranian authorities said that the strait was open. Iran later reversed course, after President Trump said that a U.S. naval blockade of Iranian ports in the region would continue.

In recent weeks, 1,600 or more vessels have been stranded in the waters around the Strait of Hormuz, after the U.S. and Israel attacked Iran, leading to major disruption to the flow of traffic through the crucial waterway. Very few vessels operated by European or U.S. companies have been able to navigate the strait because of the risk of sea mines and attacks by Iran.

Wybcke Meier, the chief executive of TUI Cruises, thanked the captains and crews of the two stranded ships. “The past few weeks have presented us all with extraordinary challenges,” she said in a statement.