He added that the trade deal would "put millions of people to work, create new jobs, more opportunities and it is worth pushing for."

Trade officials from the EU and US will resume the second round of negotiations in Brussels next week, with discussions on services, investment, energy and regulatory issues.

The talks remain a priority for the European Commission in the final months of its mandate.

It estimates that a transatlantic trade partnership could be worth €120 billion a year to European economies if negotiations go well.

But Kerry's statement comes amid European concern the US could have inside knowledge of EU mandates and tactics due to its spying activities.

Revelations by US leaker Edward Snowden indicate the NSA is not just snooping on millions of ordinary EU citizens, but has also bugged EU embassies and EU leaders, including German Chancellor Angela Merkel.

France and Germany recently set out plans for a new rulebook on espionage with the US, while President Barack Obama has ordered a review of his intelligence services.

But some top EU officials, such as European Parliament chief Martin Schulz, have said the trade talks should be halted until the NSA affair is cleared up.

Kerry told reporters in Warsaw the US government would work with European counterparts to "strike the right balance between protecting our citizens and, obviously, the privacy of all our citizens."

He added: "We can not only alleviate concerns, but we can actually strengthen our intelligence relationships going forward."

For his part, Sikorski, a keen atlanticist, also warned EU lawmakers against linking free trade with the NSA scandal.

“These are two separate things," he said.

"One [free trade] belongs to Europe itself, to the community. The second one is rather national in character, it depends on individual states vis-a-vis the US," he added.