KABUL (CNN) -

U.S. Secretary of State John Kerry arrived in Austria on Sunday for talks with five other world powers and Iran on Tehran's nuclear program.

The participants will hold a final round of negotiations ahead of a July 20 deadline aimed at reaching a permanent deal on the future of Iran's nuclear program.

"Obviously, we have some very significant gaps still, so we need to see if we can make some progress," Kerry said in the Austrian capital, Vienna. "I really look forward to a very substantive and important set of meetings and dialogues."

The nuclear talks will include the five permanent members of the United Nations Security Council -- the U.S., UK, France, China and Russia -- and Germany.

"It is vital to make certain that Iran is not going to develop a nuclear weapon, that their program is peaceful," Kerry said.

Tehran insists its ambitions are peaceful, but the world powers fear it plans to build nuclear weapons.

"We don't see any benefit in Iran developing a nuclear weapon," Iran's Foreign Minister Javad Zarif told NBC's "Meet The Press" from Vienna.

He said Iran has a number of advantages over its neighbors, including "the fact that we have better technology," which Iran doesn't need to augment with nukes.

"I believe nuclear weapons reduces countries' influence in our region," he added. "It doesn't help anybody."

Israel's Prime Minister Benjamin Netanyahu, speaking on "Fox News Sunday" from Jerusalem, called Zarif's comments a "joke" and a "sham." He said Iran has invested billions into its nuclear program.

"For what? For creating medical isotopes for Iranian patients circling the earth? What are they developing ICBMs for if not for nuclear warheads?" he asked. "What are they developing these -- building these enormous underground nuclear facilities, if not for a nuclear weapon?"

Kerry is expected to meet with Zarif on Sunday night.

Kerry seeks to mend U.S.-German relations

Kerry met Sunday in Vienna with his German counterpart, Frank-Walter Steinmeier. The encounter came amid a row over fresh spying allegations against the United States.

On Thursday, Germany's government asked America's top spy chief stationed in the country to leave.

This followed the revelation that two Germans -- one working at a German intelligence agency, the other in the Ministry of Defense -- are suspected of spying for the United States.

After Sunday's meeting, Kerry described the relationship between the two countries as "a strategic one. We have enormous political cooperation, and we are great friends and we will continue to work together in the kind of spirit that we exhibited today."

Kerry did not address the spy flap in his public remarks after the meeting, saying instead the conversation focused on Iran and also included Afghanistan and Iraq.

Kerry: Afghanistan election audit coming

Kerry's stop in Austria follows an unannounced visit to Afghanistan, where divisions are growing since the country's contested presidential runoff election.