July 16 (Bloomberg) -- A top State Department official will attend nuclear negotiations between Iran and the European Union, in a shift of the U.S. position on talks with a government it has shunned for almost three decades.

Undersecretary of State William Burns will join a meeting scheduled for July 19 in Geneva between EU foreign policy chief Javier Solana and Saeed Jalili, Iran's nuclear envoy, White House spokeswoman Dana Perino said. Burns will reiterate that Iran must suspend uranium enrichment and reprocessing before formal talks can begin, she said.

``This is a new tactic,'' Perino told reporters at the White House today. ``There is no negotiation here.''

The move breaks with the Bush administration policy of refusing to participate in even preliminary discussions with Iran over its nuclear program until it suspends uranium enrichment, a process that can produce energy or an atomic bomb. Tensions intensified, helping push oil prices to a record, after a June 2 Israeli military exercise that analysts saw as a rehearsal for a strike on Iran, and following Iranian missile tests last week.

The U.S. wants to signal to the Iranian government and its people as well as European and United Nations partners in the talks that it is committed to a diplomatic solution, State Department spokesman Sean McCormack said.

President George W. Bush approved of the plan to send Burns to the meeting, Perino told reporters at the White House.

`Pressure'

``Iran is feeling a little pressure,'' she said. ``This meeting will also further clarify the consequences, which are more sanctions, if Iran doesn't accept the incentives package.''

In the meeting with Solana, Jalili is to give Tehran's formal response to a sweetened offer of economic and diplomatic incentives offered last month by the U.S., Britain, France, Germany, Russia and China.

Democratic presidential candidate Barack Obama applauded Burns's plan to join the meeting with Iran.

``Now that the United States is involved, it should stay involved with the full strength of our diplomacy,'' Obama said today in a statement. ``A united front with our friends and allies directly calling on the Iranians to stand down on their illicit nuclear program will maximize the international pressure.''

Hostage Crisis

The U.S. broke off relations with Iran five months after 52 diplomats at the American Embassy in Tehran were taken hostage by students involved in the 1979 Islamic revolution that ousted Shah Mohammad Reza Pahlavi.

Burns's participation is a one-time event to show that the five permanent UN Security Council members, plus Germany, are united and to reinforce Secretary of State Condoleezza Rice's signature on the incentives package, Perino and McCormack said. Burns won't meet separately with Jalili, they said.

The U.S. initiated the idea of Burns attending the meeting and notified ``a number of diplomatic partners,'' McCormack said. He declined to say whether one of them was Israel, which Iranian President Mahmoud Ahmadinejad has threatened to wipe ``off the map.''

Mixed Signals

Mixed signals from public statements by Iranian officials on whether the country should accept the incentives indicated Tehran might be more open and prompted the reappraisal of how to address negotiations, McCormack said.

``Perhaps this is a new opening, or this is reflecting a sea change in the policy that the U.S. is using'' on Iran, said Christopher Pang, head of the Middle East and North Africa program at the Royal United Services Institute in London. ``Perhaps they're realizing that isolating Iran is not the way forward, and at some stage you have to engage with the country.''

Burns signaled to Congress last week that the Bush administration might be open to more direct engagement with Iran. He cited talks that led Libya to renounce terrorism and give up weapons of mass destruction, and the negotiations with North Korea that are ``beginning to produce results.''

``It may or may not produce results on Iran,'' Burns said in testimony to committees in the House and Senate. ``But it is important for us to try.''

Blockade

Iran has said it may blockade the Strait of Hormuz as a last resort if its nuclear sites are attacked. About a fifth of the world's daily oil supply is shipped through the chokepoint, between Iran and Oman at the mouth of the Persian Gulf. The U.S. carried out naval maneuvers on July 7 to practice protecting Gulf oil rigs and said it won't allow the strait to be closed.

The Geneva talks also will focus on a possible formula under which Iran would stop expanding its atomic activities and the international community would delay further sanctions, an official said on condition of anonymity.

This ``freeze-for-freeze'' phase would last a maximum of six weeks with the goal of preparing for full negotiations over the incentives offer, Burns told Congress last week.

Iran's supreme leader, Ayatollah Ali Khamenei, said today that his country won't bow to any threat made during negotiations, the state news agency IRNA reported.

``The officials of the country will continue talks,'' IRNA cited Khamenei as saying. ``The condition, however, is that nobody threatens the Iranian nation.''

To contact the reporters on this story: Roger Runningen in Washington at rrunningen@bloomberg.netViola Gienger in Washington at vgienger@bloomberg.net;

Last Updated: July 16, 2008 14:41 EDT