Ukraine announced Monday it will give up its weapons-grade uranium at the ongoing Nuclear Security Summit, which is attended by leaders and senior officials from 50 countries and international organizations.

U.S. President Barack Obama, the host, applauded the move. "It's impressive. I think it's an indication of how deeply concerned everybody should be with the possibilities of nuclear traffic, and I think at the end of this we're going to see some very specific, concrete actions that each nation is taking that will make the world a little bit safer," Obama said.

Obama is hosting leaders from 47 countries, the United Nations, the European Union and the International Atomic Energy Agency for a two-day nuclear security summit that is focusing on how to better safeguard weapons materials, both old and new, to keep them out of the hands of terrorists.

Already, there have been significant achievements. As is already public, Chile has removed all of the highly-enriched uranium from the country. There has also been recent benign interaction between the United States and Russia, which possess 90 percent of the world's nuclear weapons.

China, one of the major countries in the world, attaches great importance to the issue and the summit as well.

Chinese President Hu Jintao will deliver a speech stressing the importance of nuclear security and clarifying China's policy on the issue.

"We hope common ground can be increased between all participants, and that they will pay greater attention to nuclear security, and work together to safeguard international peace and security," Chinese Deputy Foreign Minister Cui Tiankai said last week.

China also hoped the summit would promote international cooperation to ensure the safety of nuclear materials and facilities, as well as the peaceful use of nuclear energy, according to Cui.

However, despite the pledges and efforts of many countries to prevent the smuggling and acquisition of nuclear materials by terrorist groups and "non-state actors," the world still faces a tough situation in this regard.

Seeking to highlight the urgency of the threat posed by terrorists in pursuit of a nuclear bomb, John Brennan, the White House's counterterrorism chief, told reporters Monday that al-Qaida is actively in search of the key ingredients for a bomb and the expertise to assemble it.

He said such an improvised device could be obtained through criminal gangs or by infiltrating nuclear labs in Pakistan or other nuclear nations.