Buenos Aires, July 14 (Reuters) - Argentina's central bank on Thursday announced a change in its strategy for setting the country's interest rates, which have risen sharply since the beginning of the year as the bank struggles to combat surging inflation.

Rates will now be set according to a range defined by three variables: the interest rate on short-term Treasury bills, the benchmark 28-day Leliq rate, and the overnight rate, according to a statement.

The central bank's overnight rate will act as the lower bound and the rate on Treasury bills will be the upper limit.

Under the bank's former policy, the 28-day Leliq was the only determinant of the benchmark rate.

The decision seeks to "achieve a scheme of positive interest rates in real terms for the economy," the central bank said.

Argentina has pledged to adopt positive real interest rates as part of its credit agreement with the International Monetary Fund.

A spokesperson for the central bank did not immediately reply to Reuters' inquiries. (Reporting by Nicolas Misculin; Writing by Valentine Hilaire; Editing by Leslie Adler)