London - Britain's top share index climbed to a two-week high on Wednesday, with a rise in mining and energy stocks on the back of firmer commodity prices and a rally in retailers supporting the market.

The blue-chip FTSE 100 index was up 0.4 percent at 6,858.97 points by 08h07 GMT after rising to 6,861.66 points, the highest level since June 11.

Miners were in demand, with the UK sector index rising 1.1 percent, tracking a 0.2 to 0.5 percent gain in major industrial metals such as copper and aluminium.

“A rise in metals prices and recent data showing an improvement in Chinese manufacturing are providing a tailwind to the market, but investors will continue to be cautious as we haven't yet seen a firm direction for commodity prices,” said Keith Bowman, equity analyst at Hargreaves Lansdown.

The UK oil and gas index gained 1.3 percent, the top sectoral gainer, after oil prices rose on hopes for stronger than expected US crude demand, while doubts over the prospect of reaching an agreement next week on Iran's nuclear programme eased oversupply concerns.

Shares in BG Group, Royal Dutch Shell, Anglo American, BHP Billiton and Rio Tinto rose 1.2 to 1.7 percent.

Investors also showed interest in retailers after a positive sector note from Societe Generale. J. Sainsbury rose 2.4 percent to 275.7 pence, the top gainer in the FTSE 100 index, after the bank raised its stance on the stock to “buy” from “hold” and lifted its target price to 315 pence from 260 pence.

“We think that the group's profile is more resilient than many fear, thanks to its strong differentiation (clear focus on quality and in-store services) and efficient marketing policy,” Societe Generale analysts said in the note.

Shares in Tesco and Morrisons rose 1.2 percent and 2.3 percent respectively.