The United States remains interested in a possible purchase of light attack aircraft made by Brazil's Embraer despite cancelling a contract this week, a top US official said Thursday.

Deputy Secretary of State William Burns, on a visit to Rio de Janeiro, said the contract cancellation was not a reflection on the Super Tucano -- to be used in Afghanistan -- which he described as "a very fine aircraft."

Brazil's foreign ministry issued a strongly-worded statement, voicing its "surprise" at the cancellation of the bid, particularly "its manner and timing."

"This development is not considered conducive to strengthening relations between the two countries on defense affairs," the terse statement said.

The Pentagon cancelled Tuesday a $355 million contract with US firm Sierra Nevada Corp. and Brazil's Embraer, and announced an investigation after a legal challenge from rival American aerospace firm Hawker Beechcraft Corp.

"Embraer is a great company and the Super Tucano is a very fine aircraft," Burns told reporters in Rio. "The US is now in the midst of some internal processes but we remain interested."

Burns said there was no link between that contract and a tough bidding war in Brazil for 36 air force fighter jets. US-based Boeing is battling for the deal worth between $4-7 billion with France's Dassault and Swedish maker Saab.

"They are two separate issues," Burns said.

"We're convinced that the (Boeing) F18 is the best available aircraft. One thing that reflects that is that it's the aircraft the US is going to be using for the next 20 or 30 years," he said.

"We're convinced that the technology transfer package that we're offering along with that aircraft is unprecedented in our relationship and is also the best of the available packages."

On the Embraer contract, US General Norton Schwartz said Wednesday that the Air Force would move "quickly" to relaunch the contest for 20 light support planes for the Afghan military as funds for the program will expire at the end of fiscal year 2013.

The contract for 20 Embraer AT-29 Super Tucano aircraft was awarded in December as part of plans to arm the Afghan military amid a NATO troop drawdown.

But the US Air Force said it was not "satisfied" with the paperwork and announced a review of the award.

The US military wants to provide a light aircraft for Afghanistan's air fleet to conduct flight training, aerial reconnaissance and combat support operations for ground troops.

The AT-29 Super Tucano is a turboprop aircraft designed for low-threat environments.

However Hawker Beechcraft Corp, based in Wichita, Kansas, protested the award, arguing that its AT-6 plane was unfairly shut out of the competition.

Embraer officials denied the allegations but were unable to stop a government investigation.