LONDON, June 17 (Reuters) - London-listed platinum miner Lonmin Plc moved to cash in its investment in AngloGold Ashanti on Thursday, announcing plans to sell a further 2.63 percent stake in the African gold miner.

Lonmin, which also operates in Africa, sold 3.5 million shares in AngloGold Ashanti to mining giant Anglo American Plc, AngloGold's main shareholder, on June 4.

On Thursday, Lonmin said the fresh sale of 6.94 million shares would be carried out by way of a bookbuilding exercise targeted at institutional investors.

AngloGold shares were down 1.9 percent to 196.70 rand at 1120 GMT after earlier falling as much as 3.7 percent to their lowest level since May 2003.

Lonmin had a nearly 28 percent stake in Ghana-based Ashanti Goldfields, which was acquired by AngloGold last April in an all-share deal, which gave it 10.44 million shares in the enlarged company.

The firm said Anglo American had committed to purchase a further 2.7 million shares in the bookbuilding, which would be allocated to the world's third-biggest diversified miner in full at the offer price on closing.

Anglo's stake in AngloGold was diluted to around 47 percent from 54.5 percent following the Ashanti takeover, but the firm has always said that it will seek to rebuild a stake of over 50 percent in AngloGold.

Investment banks Cazenove & Co and JP Morgan Securities are the joint bookrunners to the offering.

Lonmin, whose shares were up nearly two percent at 983 pence by 1100 GMT, said the bookbuilding was expected to close later on Thursday, with pricing and allocations expected early Friday.