JAKARTA- Indonesia's PT Pertamina and Saudi Aramco have extended negotiations regarding an upgrade to Pertamina's Cilacap oil refinery December, State-Owned Enterprise Minister Erick Thohir said on Tuesday.

The two sides have extended their negotiations a few times since last December as they struggle to agree on a valuation for the project. A financial adviser they have hired has not yet produced a valuation, Thohir said.

Thohir said the government wants Pertamina to work on the Cilacap refinery upgrade with Aramco, but is open to alternative partners should they fail to reach a deal.

"We are trying to have an agreement this year, that's what they are pushing for," Thohir, who was appointed as minister by President Joko Widodo last week, told reporters.

A Pertamina official in April said that if a deal with Aramco is not reached, the state-run company is prepared to launch the project on its own to meet its 2025 operational target.

Pertamina and Aramco first agree to form a joint venture to upgrade the Cilacap refinery in Central Java province in 2016.

(Reporting by Wilda Asmarini; writing by Fransiska Nangoy; editing by Jason Neely) ((Fransiska.Nangoy@thomsonreuters.com; +62 21 2992 7610; Reuters Messaging: fransiska.nangoy.thomsonreuters.com@reuters.net))