Vietnam has announced an 8.5-billion-dollar economic and defence development plan for a string of islands along its resource-rich coastline, as a broader sovereignty dispute simmers with China. A copy of the plan, dated April 28, was obtained by selfnews on Tuesday. It calls for development over a 10-year period of a string of islands stretching from Phu Quoc near Cambodia in the southwest, to Cat Ba off Haiphong in the north near China. Authorities aim to boost seafood, tourism, agro-forestry and other sectors under the plan, which will require an estimated investment of 162.5 trillion dong (8.5 billion dollars) over 10 years to 2020, the document says. It also calls for increased investment in the islands' defences. 'It is essential to pay attention to security and defence tasks during arrangements for economic and civil projects on islands,' the document says, calling for them to become an 'outer defence stronghold'. The stronghold would include the Spratlys, the document says, although the South China Sea archipelago is not among the islands listed for the economic development initiative. Vietnam and China are engaged in a long-running dispute over sovereignty of the Spratlys and another archipelago to the north, the Paracels, which China occupies. The archipelagos are considered strategic outposts with potentially vast oil and gas reserves, and rich fishing grounds. Taiwan also claims the Paracels while the Spratlys are claimed in full or in part by China and Vietnam as well as the Philippines, Malaysia, Brunei and Taiwan. Over the past year Vietnam has reported cases of fishing boats and equipment being seized by China. Among the islands included in Vietnam's development plan are Phu Quy and Con Dao, off southern Vietnam where the country already produces oil and gas. In December, Vietnam reached a major arms deal with Russia that was reported to involve the purchase of six submarines. Analysts said the deal aimed to bolster Vietnam's maritime claims against China. 