"We will continue to designate entities as we find them trying to use the international financial system for their ill-gotten games," she said during a plane ride to California with British counterpart David Miliband.

"And yes, we are going to continue to do it and we are going to continue to do it aggressively."

Iran has said it is ready to enter "serious and targeted" negotiations with world powers on a wide range of issues, including nuclear energy,

In a package, attached to a May 13 letter from Iran's foreign minister to UN Secretary General Ban Ki-moon, the Islamic republic offered talks on nuclear disarmament and the peaceful use of atomic technology, according to the translation posted on the website of the Institute for Science and International Security (ISIS).

But Iran's proposal to six world powers -- the United States, France, Britain, Russia, Germany and China -- does not include any promise to halt uranium enrichment work, which it has continued in defiance of UN sanctions.