UPDATE 1-Indonesia police tighten net on illegal miners

(Adds analyst comments, updates prices)

By Lewa Pardomuan and Fitri Wulandari

LONDON/JAKARTA, May 28 (Reuters) - Indonesian tin miners have kept a low profile as police step up vigilance against illegal miners, curbing supplies and helping prices firm.

Tin powered to an all time high of $25,500 a tonne on the London Metal Exchange in mid-May in another round of speculative buying driven by supply worries from main producers China and Indonesia as well as low inventories.

Indonesia is Asia's largest tin exporter, with main producer China becoming a net importer in 2008 to meet local demand for tin used in electrical solder and as anti corrosion.

"Local mining office has tightened checks on shipments around Bangka-Belitung islands. They will check your shipping licences and the origin of the ore," said Ismiyardi, commissioner of Bangka-Belitung Timah sejahtera, a consortium of 10 smelters.

Since a crackdown on illegal mining on the main producing islands of Bangka and Belitung in late 2006, which led to the closure of unlicenced smelters and a drop in exports in 2007, markets are closely watching developments in Indonesia.

Two subcontractors for the country's second-biggest tin smelter, PT Koba Tin, are on trial on Bangka for deliberately selling illegally mined tin ore to the company.

"Police will impound the ship if there's no proper documents. Our ore supplies are tight because of the policy. We don't want to flood the market. We are careful about our production when the prices are high," said Ismiyardi.