WASHINGTON, Sept. 18 (Xinhua) -- U.S. Secretary of State Hillary Clinton said Friday that Tehran must decide whether to accept offer from world powers on its nuclear issue, saying Iran's defiance will lead to "more isolation and economic pressure."

    "There will be accompanying costs for Iran's continued defiance: more isolation and economic pressure, less possibility of progress for the people of Iran," the top U.S. diplomat said in a speech at the Brookings Institution, a think tank based in Washington.

    "We have made clear our desire to resolve issues with Iran diplomatically. Iran must now decide whether to join us in this effort," she said.