NEW DELHI, June 28 (Reuters) - India's infrastructure output in May rose 6.3% year-on-year, compared with a revised upward growth of 6.7% in April, government data showed on Friday, backed by coal and electricity output.

Infrastructure output, which accounts for 40% of industrial production, measures activity in eight sectors, including refinery products and electricity.

Coal production in May grew 10.2%, while electricity generation rose 12.8%. In April, coal production rose 7.5% and electricity generation grew 10.2%.

Steel production grew 7.6% year-on-year in May, against an 8.8% increase a month earlier. Natural gas output registered a growth of 7.5% in May, while it rose 8.6% in the previous month.

Refinery products rose 0.5% against a 3.9% rise in the previous month.

However, cement, crude oil and fertiliser output fell in May.

While cement production fell 0.8% in May, compared with April's 0.5% drop, crude oil production was down 1.1%, compared with a 1.6% growth in April.

Fertiliser production saw a fall of 1.7% in May, compared with a fall of 0.8% in April. (Reporting by Shivangi Acharya and Nikunj Ohri; Editing by Sohini Goswami)