(Adds details on share buyback, outlook)
Sept 11 (Reuters) - Industrial equipment rental firm Ashtead Group Plc expects full-year earnings to beat its previous expectations after a 20 percent rise in profit in the first quarter on the back of higher margins and revenue at its U.S. business.
The company said in its first-quarter report on Tuesday that it plans to raise share buybacks to 125 million pounds ($163.2 million) per quarter, bringing the total under a programme announced in December 2017 to 675 million pounds.
The programme will be extended into the financial year 2019/2020 with an anticipated spend of at least 500 million pounds, Ashtead added.
The FTSE 100 firm, which gets 84 percent of its revenue from its Sunbelt U.S. business, said the first quarter benefited from better margins, lower equipment replacement capital expenditure and weaker sterling.
"With the benefit of weaker sterling, we expect full year results to be ahead of our expectations and the board continues to look to the medium term with confidence," the company said.
Asked afterwards by Reuters, a company spokesman said the guidance referred to profit.
Underlying pretax profit at the company, which rents diggers, construction tools and other industrial equipment, rose to 285.6 million pounds for the quarter ended July 31, from 238.5 million pounds a year ago, it said on Tuesday.
Rental revenue rose 16 percent to 961 million pounds as its U.S-based construction and industrial equipment rental division, Sunbelt U.S, posted a 20 percent rise in revenue to $1.17 billion. ($1 = 0.7659 pounds) (Reporting by Shashwat Awasthi and Justin George Varghese in Bengaluru; editing by Patrick Graham and Amrutha Gayathri)