SEOUL, South Korea — Somali pirates warned a South Korean destroyer chasing a hijacked supertanker with 24 sailors on board not to get any closer or else risk endangering the crew, Seoul’s Foreign Ministry said Thursday.

All crew members of the South Korean-operated, Marshall Island-flagged Samho Dream are safe, the pirates said by phone Wednesday through the tanker’s captain in the first contact since the hijacking Sunday in the Indian Ocean.

However, “the safety of the sailors will be in jeopardy” if the destroyer sails any closer, the pirates warned, a ministry official said.

Pirates have been on a streak of ship hijackings in recent weeks, with at least 16 ships and some 240 crew members believed held captive off Somalia’s lawless coast.

Somalia has not had a functioning government since 1991, and multimillion-dollar ransoms have become a way to make money in the impoverished nation.

On Wednesday, pirates hijacked a Turkish vessel with a crew of 25 off the Kenyan coast, according to the EU Naval Force. Separately, a hostage on board the hijacked Indian cargo dhow Faize Osamani drowned Tuesday when the ship was used to attack another vessel and navies intervened.

The Samho Dream was loaded with about $160 million in crude oil when it was hijacked. A South Korean naval destroyer on anti-piracy patrol took off in pursuit of the 300,000-ton tanker and caught up with it the next day, officials in Seoul said.

The captain said the pirates are “heavily armed” and warned that they should not be provoked since the tanker is carrying a large amount of crude oil, South Korea’s Foreign Ministry said.

The hijackers demanded direct contact with the ship’s owner but formal negotiations over the crew’s release have not begun, a ministry spokesman said. The crew includes five South Koreans and 19 Filipinos.