From CNN Foreign Affairs Correspondent Jill Dougherty

WASHINGTON (CNN) – Secretary of State Hillary Clinton stressed Wednesday that the White House remains open to diplomatic engagement with the Iranian government if Tehran is serious about negotiations regarding its controversial nuclear program.

"If Iran is serious about taking practical steps to address the international community's deep concerns about (the) program, we will continue to engage both multilaterally and bilaterally to discuss the full range of issues that have divided Iran and the United States for too long," she said.

"The door is open to a better future for Iran. But the process of engagement cannot be open-ended. We are not prepared to talk just for the sake of talking."

Clinton made her remarks during a wide-ranging speech on nuclear non-proliferation at the U.S. Institute of Peace, a non-partisan think tank.

Tehran says its nuclear program is intended solely for peaceful purposes.

But many in the West believe Iran is pursuing nuclear weapons capabilities.

The Obama administration is working on a substantial sanctions package against Iran in case current diplomatic efforts to curb its nuclear program fail, top officials told Congress earlier this month.

Negotiators recently hammered out the details of a tentative deal calling for low-enriched uranium produced in Iran to be sent abroad for further enrichment and then returned for use in medical research and treatment.

Clinton's address touched on U.S. policy in a range of hot spots around the globe, including North Korea, Pakistan, and Russia.

Among other things, Clinton said the United States is prepared to meet with North Korea. Current sanctions will not be relaxed, however, until Pyongyang takes verifiable, irreversible steps to dismantle its nuclear
program, she added.

The State Department recently decided to authorize visas for a North Korean nuclear delegation so members can attend conferences in the United States later this month.

North Korea pulled out of talks in April in protest of the United Nations' condemnation over its nuclear test and missile launches.

Turning her attention to central Asia, Clinton said Pakistan's embattled government has reassured administration officials that, despite a recent spate of attacks by militants, its nuclear stockpile remains secure.

While the attacks do not pose a threat to Pakistan's nuclear weapons, she noted, U.S. officials "have asked a lot of questions" of the Pakistani government.

The secretary also hit back against domestic critics of the administration's willingness to negotiate a new START arms control agreement with Russia.

The United States is interested in a new agreement because it will bolster American security, she asserted. "Clinging to nuclear weapons in excess of our security needs" will not protect the United States, she said.

Clinton called for an expansion of the Nuclear Nonproliferation Treaty and appealed for ratification of the Comprehensive Nuclear Test Ban Treaty by the Senate. She conceded the administration has its "work cut out" in winning approval, but argued it is "the right thing to do." The secretary noted that the U.S. government is already is observing a moratorium on nuclear testing.

Finally, Clinton pushed for passage of the Fissile Material Cutoff Treaty, which would ban the production of fissile material for nuclear weapons.

Congress has yet to approve the measure.

She warned that "vast stocks of potentially vulnerable nuclear material remain vulnerable to theft and diversion."

There is a danger of a world with a "steadily growing number of nuclear states and terrorists getting their hands on nuclear material," she said.