Speaking in Warsaw after talks with Poland's foreign minister, Kerry said Tuesday that Europeans and others have "legitimate" questions about the surveillance and that those would be answered in private diplomatic discussions.
"We need to understand that we are all in this together," Kerry said. "We are all in the effort to be able to provide protection to our citizens. And we have to strike the right balance between protecting our citizens and obviously the privacy of all our citizens. That is a balance that we do try to strike."
Polish Foreign Minister Radoslaw Sikorski said he had spoken with Kerry and "we have agreed on closer cooperation between our services on combatting common threats."
Poland has announced plans for major investments to improve its armed forces - one of few NATO countries to heed U.S. calls to expand and upgrade its military.
Kerry made clear in his news conference with Sikorsky in Warsaw and a brief visit to the Lask Air Base in central Poland that U.S defense contractors will be competing intensely for major parts of the $45 billion upgrade.
Sikorski also said that trade issues should be separate from surveillance questions.
"These are two separate things, two separate orders. One belongs to Europe itself, to the community," he said. "The second one is rather national in character, it depends on individual states vis-a-vis the U.S."
Kerry said President Barack Obama had ordered a complete review of NSA's activities. But Kerry said it is important that concerns over NSA and other activities did not affect discussions about the Trans-Atlantic Trade and Investment Partnership. Some European officials have said the surveillance issue may have a negative impact on the negotiations.
The European Commission, the 28-nation bloc's executive arm, said Monday that the talks will go ahead and that next week's round in Brussels is set to focus on services, investment, energy and regulatory issues.
A broad EU-US trade deal could provide a boost to growth and jobs on both sides of the Atlantic by eliminating tariffs and regulatory barriers that are hampering business. The trade volume in goods and services between the two economies - representing almost half of global output - totaled 800 billion euros ($1.08 trillion) last year.
But trade discussions are taking place under a cloud following revelations over the NSA's alleged spying activities including eavesdropping on German Chancellor Angela Merkel's phone. Some top European lawmakers have called for the talks to be suspended.
Kerry said it was important to keep the trade talks separate from "legitimate questions" about NSA and other activities.
"This is about jobs, it's about the economy, it is about economic competition in a global community that competes, sometimes by rules that are very questionable and shaky," Kerry said.
Kerry, the most senior Obama administration official to visit Europe since revelations of NSA spying sparked major outrage across the continent, emphasized that the U.S. understood its allies' concerns.
"We want to hear from our allies, we want to have this conversation," Kerry said. "President Obama welcomes this opportunity to work with our allies. And, ultimately, if we get it right, which we will, we will not only alleviate the concerns but we can actually strengthen our intelligence relationships going forward."
Associated Press writer Monika Scislowska in Warsaw, Poland contributed to this report.