China restructured billions of dollars in Cuba debt over the last six months and agreed to provide new credit in a clear show of support for President Raul Castro’s efforts to reform the economy, Asian diplomats said.

Beijing and Havana signed an accord last summer restructuring government debt, and more recently restructured commercial debt, with principal in both cases not coming due until after 2015 and on easy terms, the diplomats said, without providing further details.

Figures haven’t been released, but Cuba’s official and commercial debt to China may be as high as $4 billion, say government insiders.

As part of the accord, China will continue to provide trade cover and both parties agreed to use an already existing development credit to modernize the port of Santiago de Cuba, 800 miles east of Havana, the diplomats said. Bilateral trade came to $1.5 billion in 2009, down significantly from $2.2 billion in 2008.