The pace of deforestation in Brazil's Amazon basin fell 18 percent over the past year, the government said Wednesday, dismissing as speculation reports of a huge increase in forest loss last month.

Environment Minister Izabella Teixeira said deforestation from August 2013 to July 2014 amounted to 4,848 square kilometers (1,870 square miles), the second lowest figure on record.

A non-government group, Imazon, last week warned of a 467-percent rise in October from the same month a year earlier.

But Teixeira said the official estimate was the most accurate.

"Anything else is speculation. We have been working hard to end deforestation," she said.

She presented the figures just days before the Lima Climate Change Conference, which opens Monday.

The government measure covers Brazil's nine Amazonian states using the Brazil's Space Research Institute's satellite forest clearing detection service PRODES.

The 2011-2012 figure of 4,571 km2 was the lowest on record. Although the following year saw a 29 percent increase to 5,891 km2, official sources insist the underlying trend now is downward.

Referring to Imazon's October figure, Teixeira told reporters: "There is much speculation. There are systems such as that of Imazon speculating on an increase. Now there is an official figure."

Brazil recently announced it was adopting a new satellite alert system to counter deforestation in the Amazon, the world's largest forest, which covered 27,000km2 in 2004.

But Imazon said in a statement it worried that its figures suggested the government's efforts were not proving effective enough.

Imazon's estimates suggested a loss of the equivalent of 24,000 football pitches.