The head of the National Broadband Network (NBN) has rejected suggestions he timed a major announcement about faster downloads speeds to have maximum impact on the federal election.

The Government this morning confirmed the network will be able provide downloads at up to 1 gigabit a second - which is 10 times faster than originally planned.

The top speed is also nearly 100 times faster than the minimum speed promised under the Coalition's alternative broadband scheme.

But NBN co-chief executive Michael Quigley says there is nothing suspicious about the timing of the announcement.

"We in fact made this decision to go to 1 gigabits... after some considerable study we decided, 'What do we do? We sit on it because there's an election on?'," he said.

"Or do we do what we normally do, which is to announce it to the industry. I decided the right thing to do was to announce it to the industry."

Mr Quigley says the total cost of the project will not exceed the $43 billion upper limit estimated by the Government.

"In moving to 1 gigabits per second we haven't increased the cost of the network at all, it was just a question of dimensioning and what was available on given ports and how we would do that," he said.

"There is no extra cost implications on the network on going to 1 gigabit."

Communications Minister Stephen Conroy was quizzed on whether it was known all along that the network was able to deliver much faster speeds than the originally announced 100Mbps.

"The announcement by NBN Co to increase capacity on the network shows that fibre technology is truly about future-proofing the nation," he said.

"They're now confident, that they've actually robustly tested it, that the interfaces can sustain the gig."

Opposition Leader Tony Abbott says he doubts the Government's claim of super-fast speeds.

"This idea that, hey presto, we are suddenly going to get 10 times the speed from something that isn't even built yet, I find utterly implausible," he said.

Prime Minister Julia Gillard used the NBN announcement to attack the Coalition's decision to scrap the network.

"I am completely determined that we will build the NBN," she said.

"I will build the NBN. Mr Abbott, if he is elected as PM, will not. That decision would cost Australia jobs."

The Government says the NBN will provide fibre-optic connections to 93 per cent of the population. The remainder would receive wireless or satellite technology.

The Coalition also revealed its broadband policy this week, pledging to spend $6 billion to deliver internet speeds of between 12Mbps and 100Mbps to 97 per cent of Australians through a range of technologies.

The Coalition has vowed to dump the NBN because it says it is too expensive and it does not support a nationally owned network.