Brazilian state-run oil firm Petroleo Brasileiro SA posted a significant production boost in the third quarter, as heavy investments in its deepwater, pre-salt zone showed signs of paying off.

Investors and analysts have been watching the firm's production figures closely in recent quarters, and the company's ability to swiftly boost output is key to its current strategy.

In a Thursday securities filing, Petrobras, as the firm is commonly known, said it produced 2.878 million barrels of oil equivalent per day (boepd) in the third quarter, up 9.3% from the previous quarter and 14.6% from the same period a year ago.

August monthly production reached a new record of 3 million boepd, and daily production hit a high of 3.1 million boepd during the month. The company is on target to reach its annual production target of 2.7 million boepd, Petrobras added in the filing.

First quarter production at Petrobras was considered weak, and while second-quarter figures were markedly better, some analysts were spoked by poor June figures, which were affected by a number of stoppages. In late July, Chief Executive Roberto Castello Branco revised the firm's 2019 annual target to 2.7 million boepd from a previous 2.8 million, which hit Petrobras shares.

Third quarter production in Petrobras' core pre-salt region climbed 17% from the previous quarter. Post-salt production, which also takes place in deep waters, as well as onshore production remained roughly steady on a quarterly basis.

Shallow-water production increased 9.8% from the second quarter, Petrobras said, as platform stoppages were reversed.

The company said its new P-68 production platform left the shipyard in September and is currently in the anchoring process. It will begin producing in Petrobras' Berbigao and Sururu oilfields in the fourth quarter.

(Reporting by Gram Slattery and Marta Nogueira; Editing by Cynthia Osterman and Richard Pullin)