The company prospecting in the area, Cairn Lanka, a fully-owned unit of Cairn India, confirmed it informed Sri Lankan authorities of a gas discovery during its first attempt to drill into the sea floor in the Mannar Basin.
Rajapakse revealed the find while making an address to council workers in the central region of Kandy, where local elections will be held on Saturday.
“President Mahinda Rajapakse in Kandy announced that Sri Lanka has found a gas field for the first time,” the government information department said in a text message.
A presidential spokes-man said no further details were available.
However Cairn, which began exploratory drilling in August, issued a statement later on Sunday saying the discovery was made at a depth of 4,300 metres (14,000 feet) below sea level.
“Further drilling will be required to establish the commerciality of the discovery,” Cairn India, formerly a unit of British exploration firm Cairn Energy, added.
Cairn started drilling in the Mannar Basin off Sri Lanka after seismic studies suggested oil and natural gas deposits.
“The block where the discovery was made is just south of the prolific oil and gas producing Cauvery Basin (of India),” Cairn spokesman Sourav Das said.
Sri Lanka, which depends on imports for all its petroleum requirements, has also offered blocks to India and China.
Russians carried out the first drilling in the region in 1971 without any commercial success and the government subsequently abandoned the search until Norwegians helped with new seismic studies in the past decade.
London-listed mining group Vedanta Resources, led by Indian-born billionaire Anil Agarwal, has taken over Cairn India after receiving formal conditional approval from the Indian government, Das said.