FRANKFURT - U.S. carmaker General Motors GM.UL will close its Opel plant in the Belgian port city of Antwerp, sources said on Wednesday, slamming the door on hopes to save the jobs of the site's 2,300 staff.

GM has warned for weeks that the plant's future was in jeopardy as it moves to chop more than 8,000 jobs and cut European capacity by a fifth, but it had refrained until now from making a final decision.

They did not back down from the decision to close Antwerp. Now (Opel Chief Executive Nick) Reilly has announced that this would be implemented, a company source said.

Reilly has long stated his preference that the group's planned subcompact SUV would be manufactured not in Antwerp as originally planned but in South Korea by Daewoo, the GM unit where both he and Opel's new chief financial officer previously served in top management.

Daewoo is already in charge of developing GM's global subcompact Gamma platform that will underpin the future Corsa hatchback and Meriva small van.

A spokesman for the Flemish government said there was nothing new to report and said the regional authority remained committed to securing a future for the plant.

Opel and its British sister brand Vauxhall -- rescued by a German government bailout last year when GM briefly dipped into U.S. bankruptcy -- are pushing through a radical shrinking programme amid weak car markets.

The company is counting on around 2.7 billion euros (2.3 billion pounds) in European taxpayer aid for the scheme, details of which are supposed to emerge this month.

(Reporting by Angelika Gruber and Christiaan Hetzner, additional reporting by Phil Blenkinsop in Brussels; Editing by David Holmes)