A search was under way yesterday for a Greek-owned oil tanker that has not been heard from since it sent out a distress call on Thursday evening off the coast of Somalia. The Maltese-flagged San Carlos, captained by a Greek with a crew of 24, sent out the signal from a location around 170 nautical miles off the Somalian coast, the Merchant Marine Ministry said. It is feared that the vessel may have been hijacked by pirates following Wednesday's attack on another Maltese-flagged vessel, the latest in a string of hijackings in the area. Maltese and Somalian authorities have been searching for the vessel since it sent out the alert, used to indicate the occurrence of a hijacking or similarly serious incident. The San Carlos had set sail from Bahrain and was en route to South Africa, the ministry said.