WASHINGTON (CNN) -- The Bush administration has decided to break with previous policy by sending one of its most senior diplomats to engage Iran's top nuclear official, the White House announced Wednesday.

The move could dramatically alter the three-decade stand-off between the U.S. and Iran. Some western nations and Israel suspect Iran is intent on developing nuclear weapons and want Tehran to suspend uranium enrichment. Iran says it wants to develop nuclear power to produce electricity.

Undersecretary of State William Burns will accompany a European Union delegation during a meeting with Saeed Jalili, Iran's top nuclear official, in Switzerland on Saturday, White House spokeswoman Dana Perino said. The delegation meeting with the Iranians will be led by the European Union's foreign policy chief, Javier Solana.

The delegates will discuss an incentives program meant to encourage the Islamic republic to drop its nuclear enrichment program, Perino said. Watch Amanpour report on the U.S. decision to send Burns »

The U.S. decision to attend the talks is not "linked in any way" to Iran's missile tests last week, a senior administration official told CNN. The official said the meeting "had been pending before" the tests occurred. See why the U.S. is worried about Iran's missiles »

But State Department Spokesman Sean McCormack told reporters Wednesday that the president and his national security team decided only recently to send Burns to the meeting.

Perino said the "one time" participation of the United States in the meeting is meant to show the United States and other permanent members of the United Nation's Security Council are united in the "long standing principle that Iran -- in order to take advantage of the incentives package that was quite generous -- has to halt its nuclear enrichment." Watch why the White House is sending an envoy »

A group dubbed the "P5 + 1," which consists of representatives from the permanent members of the Security Council -- the United States, Britain, France, China, and Russia -- and Germany, has been negotiating over Iran's controversial nuclear program.

Secretary of State Condoleezza Rice "believes it's a smart step to take. There is no change in the substance but it sends a strong signal," McCormack said. "It sends a strong signal to our P5+1 partners. It sends a strong signal to the world. It sends a strong signal to the Iranian government that the United States is committed to diplomacy, to finding a diplomatic solution to this issue."

McCormack said Burns will be under strict orders to listen to what Iran has to say but not engage in one-on-one discussions with the Iranian negotiator.

Burns will also hammer home the point that any direct talks between the United States and Iran will occur only after Iran suspends its enrichment program, McCormick said.

"Iran needs to suspend its uranium enrichment and reprocessing related activities. Should they take that single step, the United States and its partners in the P5+1 will meet with the Iranian delegation any time, any place, anywhere to talk about a variety ... of subjects, but certainly our focus will be on the Iranian nuclear program," McCormack said.

McCormack brushed aside criticism that the United States is giving up too much to Iran.

"Is this a new tactic? Yes. Does it send a signal? Yes. Is the substance [of the U.S. position] any different? No," McCormack said.

Presidential candidate Sen. John McCain, who has said he wouldn't negotiate face-to-face with Iranian President Mahmoud Ahmadinejad without conditions, said Wednesday he had "no problem ... whatsoever" with sending Burns to Saturday's meeting with Jalili.

"We have many negotiations with many countries ... throughout the world," McCain told reporters in Nebraska, noting the U.S. ambassador to Iraq previously met with an Iranian ambassador in Iraq.

However, McCain repeated that he wouldn't meet Ahmadinejad unconditionally, noting the U.S. considers Iran a sponsor of terrorism.

"To sit down without any preconditions with a state sponsor of terror would be a mistake," McCain said.

CNN's Charley Keyes, Zain Verjee and Elaine Quijano contributed to this report.

All About Iran • Nuclear Proliferation • Condoleezza Rice