WASHINGTON, Feb. 7 (Xinhua) -- The United States on Thursday urged Iran to engage in "substantive" talks with the world powers later this month in return for eased sanctions.
State Department spokeswoman Victoria Nuland was responding to Iranian Supreme Leader Ayatollah Ali Khamenei's rebuff to Washington's offer of direct bilateral talks.
Referring to U.S. Vice President Joe Biden's suggestion last week of direct talks with Tehran over its controversial nuclear program, Khamenei told a group of Iranian military officials earlier in the day that the Obama administration has shown "ill- will" by imposing "paralyzing sanctions to paralyze the Iranian nation."
Iran has agreed to start fresh talks with the so-called P5+1 group of Britain, China, France, Russia, the United States and Germany on Feb. 26 in Kazakhstan.
In its latest effort to add more pressure on Iran, the Obama administration on Wednesday tightened up economic sanctions against the Islamic republic and adding more names to its blacklist.
"What's most important is that they come prepared to really engage on the substance," Nuland said. "The burden of these sanctions could be eased if they made a decision to engage with us substantively."
"We've always said that action on the Iranian side would be matched by action on our side, so it's really up to Iran to engage if it wants to see sanctions eased," she added.
Iran and the six powers held three rounds of talks last year but made no breakthrough.
"We've been disappointed that those have not yet resulted in real, concrete progress," Nuland said. "So as long as Iran fails to address the concerns of the international community, we're going to have to continue to increase the pressure and isolate Iran internationally."
Iran insists on the peaceful nature of its nuclear program, while the West regards it as a cover for making nuclear weapons.