Islamist fighters threatened to attack Somali pirates Sunday in an effort to rescue a Saudi oil supertanker carrying $100 million worth of crude oil that was hijacked last week, the Agence France-Presse reported.

The Sirius Star — a 1,080-foot tanker owned by Saudi Aramco — was taken captive by Somali pirates on Nov. 15 in the Indian Ocean. The pirates have demanded that a $25 million ransom be met by Nov. 30 to release the vessel.

Piracy, which is a capital offense under Islam, has reportedly angered the Shehab, a militant Islamist group that controls much of southern and central Somalia and rejects an internationally-backed peace process.

The Islamist group has threatened to launch an attack on the pirates if they do not release the tanker and has positioned their fighters in and around the city of Harardhere in recent days, according to the AFP.

"If the pirates want peace, they had better release the tanker," Sheikh Ahmed, a spokesman for the Shebab group in the coastal region of Harardhere, reportedly told the AFP by phone.

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