Officials say a Malaysian navy ship is pursuing an oil tanker hijacked a week ago and is trying to persuade armed pirates, believed to be Indonesians, to surrender.

Navy chief Abdul Aziz Jaafar said the naval ship is communicating with the captain of the tanker, and all 22 crew members are safe.

Abdul Aziz tweeted Thursday that at least eight pirates are onboard with pistols and machetes and speak with an Indonesian accent. He said the pirates have been promised they will be unharmed if they surrender.

MT Orkim Harmony, carrying gasoline worth 21 million ringgit ($5.7 million), was headed to northern Kuantan when communications were lost June 11. It was the second tanker hijacked this month in the same area.