MOSCOW, April 20 (RIA Novosti) - Iranian President Mahmoud Ahmadinejad said on Monday that the recent shift in Washington's stance toward Tehran was necessary, but that the Islamic Republic was waiting for "concrete changes."

"We are waiting for concrete changes and support a dialogue based on mutual respect," Ahmadinejad said during his opening speech at the UN World Conference Against Racism in Geneva, broadcast by Iranian state TV.

His comments came after U.S. Secretary of State Hillary Clinton said last week that Washington was striving to expand dialogue with Iran.

U.S. President Barack Obama has promised more engagement with Tehran, something that was resisted under the Bush administration.

The conference was boycotted by the U.S., Israel and a number of European countries, including Germany, over fears that the Iranian leader would launch a verbal attack on Israel. Ahmadinejad's subsequent speech, during which he called Israel a "most cruel and racist regime," sparked a mass walkout by those Western diplomats in attendance.

U.N. chief Ban Ki-moon later criticized Ahmadinejad's speech, calling it an attempt "to accuse, divide and even incite."

Iran is under three sets of relatively mild sanctions over its refusal to suspend uranium enrichment, needed both in weapons production and nuclear power generation. Russia and China, which both have a veto at the UN Security Council, have resisted harsher punishments for the country. Iran says it needs the nuclear program to generate electricity.