President Barack Obama will host his fourth and final nuclear security summit in Washington this week with tons of loose nuclear material still not sufficiently secured and still potentially accessible to terrorists or other individuals with malicious intentions.

The White House says that while it is impossible to quantify the likelihood of a nuclear attack by extremist groups, there are 2,000 metric tons of highly enriched uranium and separated plutonium with civilian and military programs around the world.

"We know that terrorist organizations have the desire to get access to these raw materials and their desire to have a nuclear device," said deputy National Security Adviser Ben Rhodes, adding that that only "redoubles" the need for international nuclear security cooperation.

For the first time, the summit will include a special session on how to ensure that groups like Islamic State do not get their hands on nuclear materials.

The biennial event Thursday and Friday will include delegations from more than 50 nations who will discuss evolving nuclear threats and ways to prevent them.

Concerns about Islamic State

The Brussels terrorist attacks March 22 signaled again how dangerous and far reaching groups like Islamic State have become. Since the attacks, Belgium has put armed guards at its nuclear facilities.

Leaders are especially concerned about the security of nuclear materials and facilities in countries such as nuclear-armed Pakistan, where a terror attack in Lahore on Easter Sunday killed more than 70 people.

While progress has been made since the first summit in 2010, "the overall objective of securing the most vulnerable nuclear materials in four years I don't think has been achieved," said Sharon Squassoni with the Center for Strategic and International Studies (CSIS). "There is still material out there and the material that we're talking about is highly enriched uranium."

Experts say security gaps remain for several reasons: There still is no international framework to monitor nuclear materials; some countries are unwilling to open up supplies intended for commercial use; and some military forces have been unable to agree on how to deal with their nuclear material.

Obama launched the nuclear summits in a 2009 speech in Prague, when he called for a world free of nuclear weapons. The U.S. policies for achieving this goal have centered on nuclear disarmament, nuclear non-proliferation, nuclear security and nuclear energy.

The White House has touted successes since then, such as the controversial Iran nuclear deal in which Tehran agreed to limit its nuclear activities in exchange for sanctions relief. It also cites more than 260 national security commitments, of which nearly three-quarters have been implemented.

Those commitments have led to the removal of nuclear materials in more than 50 facilities in 30 countries and territories, enough material for 130 nuclear weapons, the White House said. Some of those facilities were in Ukraine, Japan, Taiwan and nations across Europe and South America.

The commitments have also led to treaties being implemented, regulations strengthened and security practices improved, among other measures.

Looking at North Korea

But there have been setbacks. North Korea's continuing nuclear threat in the Korean Peninsula will be a top agenda item at the summit.

On Thursday, Obama will meet with South Korean President Park Guen-hye and Japanese Prime Minister Shinzo Abe to discuss the threat posed by North Korea and how to increase security cooperation.

"Our three countries recognize that our security is linked and that it's essential that we work closely together to meet this challenge," said Dan Kritenbrink, National Security Council senior director for Asian affairs. "I anticipate that they will call upon all in the international community to join in vigilantly implementing U.N. measures on North Korea."

Obama also will discuss North Korea's nuclear activities during a meeting with Chinese President Xi Jinping, one of numerous meetings and conversations on areas of mutual interest the two leaders have had since Xi's state visit to Washington in September.

The two also are expected to expect to discuss the sensitive issue of Beijing's increasingly expansive actions in the South China Sea, which has raised tensions among many of its neighborhoods.

"I think the high tempo of senior-level engagement with China is a recognition of the fact that this is where problems get solved and decisions get made," Kritenbrink said. "I think they'll have a candid exchange on areas where we continue to have significant differences, including things such as human rights, cyber, maritime issues, as well."

The White House announced late Wednesday that Obama will hold a "brief" bilateral meeting Thursday with French President Francois Hollande.

Later that day, the U.S. president will host a working dinner at the White House for summit leaders.

Russia's absence

Russia has declined to attend the final summit, saying the gatherings have played out their role. "We prefer that they participate constructively," said White House spokesman Josh Earnest on Wednesday.

Other U.S. officials raised concerns.

"Russia has been using increasingly harsh rhetoric with regards to nuclear policy and that has been very concerning," said Frank Rose, the U.S. assistant secretary of state for the Bureau of Arms Control, Verification and Compliance.

Olga Oliker, CSIS Director of the Russia and Eurasia Program, said Moscow's absence is linked to strained ties following Moscow's annexation of Crimea in 2014.

"They are in the midst of sending lots of signals to the United States and world that they're important, a great power and that they chart their own course," she said. "The other issue is that Russia has never been the biggest fan of this forum. It prefers broader international structures."

During the summit, the White House will try to strengthen a network of international nuclear security organizations to push ahead on the issue. Obama will meet with officials of U.N. nuclear watchdog, the International Atomic Energy Agency, Interpol and representatives of other groups to discuss advancing nuclear security cooperation.

The summit ends Friday evening with a news conference and a communique with a set of action plans "designed to support the enduring institutions and initiatives that are related to nuclear security," the White House said.

Source: Voice of America