Rio de Janeiro, Jun 3 (IANS/EFE): Brazilian state-controlled oil company Petrobras said its domestic oil output climbed 4.2 percent in April compared to the previous month to a daily average of 1.92 million barrels.

In a statement, Petrobras said the figures only included fields where the company is the operator and does not include others where it merely has an ownership stake in a block.

Including natural gas production, Petrobras' domestic hydrocarbons output in April totaled 2.31 million barrels of oil equivalent per day, up 3 percent from March. That figure also does not include output at fields operated by other companies.

Including production outside Brazil, which fell by 1.3 percent between March and April, Petrobras averaged 2.55 million boe per day in April, up 2.7 percent from the previous month.

Petrobras attributed the result to the "full return" to operation of three platforms in the Campos basin, which had been out of service after undergoing scheduled maintenance, and to increased production volumes at the Bauna field.

The Brazilian company also provided figures for the pre-salt region, saying output from those fields climbed to a record daily average in April of 293,800 barrels.

The pre-salt frontier, a series of ultra-deep oil fields that were discovered in recent years and stretch for some 800 km off the coasts of the southeastern states of Espirito Santo, Rio de Janeiro, Sao Paulo and Santa Catarina, could dramatically increase Brazil's proven-reserve tally and transform the country into a major crude exporter.

But accessing those fields, so-named because they are located under, water, rocks and a shifting layer of salt at depths of up to 7,000 meters below the surface of the Atlantic Ocean, will be very costly and pose an enormous technical challenge.