SINGAPORE, April 3 (Reuters) - Goldman Sachs has raised price forecasts for Brent crude futures following a surprise announcement from OPEC+ that the producer alliance will cut oil output further.

The price forecast for Brent for December 2023 was increased by $5 to $95 a barrel, while that for December 2024 was raised by $3 to $100 a barrel, Goldman analysts said in a note on Sunday.

The price forecast cut came as bank lowered its own end-2023 production forecast for OPEC+ - grouping the Organization of the Petroleum Exporting Countries (OPEC) and other producers including Russia - by 1.1 million barrels per day.

Brent futures surged to a near one-month high of above $86 a barrel at the start of Monday's trading following the OPEC+ announcement.

"Today's surprise (production) cut is consistent with the new OPEC+ doctrine to act preemptively because they can without significant losses in market share," the bank said.

"The risks around cutting production have become asymmetric given how short positioning has become, and because price increases in response to tightening events can be stronger when the market is short."

Goldman said that while the move was surprising, the decision reflects important economic and likely political considerations.

The bank estimated that the output reduction could provide a 7% boost to oil prices, contributing to higher Saudi Arabia and OPEC+ oil revenue.

OPEC+'s decision also came after the United States and France announced releases from their strategic petroleum reserves (SPR), the bank noted.

"The refusal to refill the U.S. SPR in fiscal year 2023, although (U.S. benchmark) WTI lows that were previously characterized as sufficient to refill, may have contributed to the OPEC+ decision to cut too," it said.