The controversial Trans-Pacific Partnership (TPP) trade agreement will go ahead and a deal is close, a senior American government official says.

Photo: Sean Gillespie

But Assistant Secretary of State Danny Russel said he could not give assurances on two aspects vital to New Zealand's interests - access for dairy products and protection for the country's medicines regime.

The TPP has been mired in years of diplomatic wrangling and protests but Mr Russel told Morning Report he was confident a deal was imminent.

"Yes, I'm absolutely confident. I have some close proximity knowledge of the absolute determination on the part of the President, the US trade representative and, frankly, the whole cabinet to get TPP done," he said.

"It's huge and we're close."

Mr Russel said the United States Congress had done its part in granting President Barack Obama Trade Promotion authority, and he did not believe any of the 12 leaders involved would have come this far without expecting to seal a deal.