At least four oil and gas tankers have turned back from attempting to transit the Strait of Hormuz, ship-tracking data showed, as renewed attacks on vessels in the critical waterway heightened safety and security concerns, Reuters reports.

LNG tankers — Al Ghariya, Duhail and Al Ruwais — have all been inching westward towards the Strait of Hormuz before changing course to turn away late on Tuesday, showed data from analytics firms Kpler and LSEG.

All three tankers controlled by QatarEnergy were empty and heading towards Qatar’s Ras Laffan export facility to load cargoes.

Meanwhile, LSEG and Kpler data also showed an Indian-flagged tanker, carrying 2 million barrels of Kuwaiti crude loaded late last week, made a U-turn off the tip of Oman at the Strait of Hormuz.