LONDON (Reuters) - Asda, the British supermarket arm of U.S. retail giant Wal-Mart (>> Wal-Mart Stores Inc), slowed the rate of sales decline in the first quarter, it said on Thursday, as its new management team started to make its mark on the business.

The UK's third-largest supermarket chain behind market leader Tesco (>> Tesco PLC) and Sainsbury's (>> J Sainsbury plc) said that sales at stores open more than a year fell by 2.8 percent, excluding fuel, in the three months to March 31, compared with a 2.9 percent decline in the previous quarter.

“We’re pleased that the momentum of Q4 has continued into the new year with a third consecutive quarter of improvement," said Chief Executive Sean Clarke.

“Despite this progress we are in no way complacent and there is still much for us to do."

Monthly industry data has also indicated an improved performance from Asda in April.

Wal-Mart veteran Clarke, who joined Asda last July, and former Sainsbury's executive Roger Burnley, who started as chief operations officer three months later, have focused their turnaround efforts on the retail basics.

They have made Asda more competitive, sharpening pricing while improving the quality and availability of product ranges and stepping up efforts to offer better customer service.

“We’re delivering more consistently for our customers, particularly in fresh food, service and availability -- both in stores and online," Clarke said.

Of Britain's big four supermarket players, which also includes Morrisons (>> WM Morrison Supermarkets PLC), Asda was hurt the most by the rise of German discounters Aldi [ALDIEI.UL] and Lidl [LIDUK.UL] and was also too slow in responding to that competition.

Separately on Thursday Wal-Mart reported higher than expected quarterly sales at established U.S. stores.

(Reporting by James Davey; Editing by David Goodman)