UNITED NATIONS, May 23 (Xinhua) -- The U.S. ambassador to the United Nations said Wednesday that his country expects to put more pressure on Iran in order to attain the Islamic republic's cooperation on its nuclear programs.

    "The time has come to take a look at additional pressure ... to bring about a change in Iranian calculations," said Zalmay Khalilzad, the 15-member Security Council's president for May.

    "The pressure so far has not produced the results we all have been hoping for," he added.

    He told reporters at the UN headquarters that council members have received the report of the International Atomic Energy Agency on Iran's compliance with UN requirements to suspend its nuclear enrichment activities.

    "We will look at the report closely ... and look forward to working with the council members to take appropriate actions with the aim of increasing the incentives of Iran to cooperate by increasing the pressure on the government," he said.

    The United States is not against Iran having a civilian nuclear program and is also open to conversations with Iran once it complies with the requirements of the Security Council, he added.

    The report of the international nuclear watchdog released Wednesday that Iran has expanded its uranium enrichment activities in defiance of UN demands to scrap its nuclear-related programs.

    The UN Security Council has passed two resolutions to impose sanctions against Iran with the aim of pressuring it to stop nuclear enrichment. The latest one, adopted on March 24, has set a deadline of late May for Iran's compliance.