U.S. President Barack Obama has warned that the threat of terrorists using a nuclear weapon has risen.
Obama said that already "terrorist networks such as Al-Qaeda have tried to acquire the material for a nuclear weapon." He called on countries to adopt a "concrete" plan to secure nuclear materials within four years.
During the summit, Ukraine and Canada announced plans to give up highly enriched uranium and produce much safer, lower-enriched uranium instead.
U.S. Secretary of State Hillary Clinton and Russian Foreign Minister Sergei Lavrov are expected to sign a deal today to implement an agreement for the two countries to each dispose of 34,000 metric tons of weapons-grade plutonium.
Leaders and top officials from more than 47 countries are attending the summit, the largest hosted by a U.S. president since 1945.
Obama announced plans for a follow-up summit to be hosted by South Korea in 2012.
compiled from agency reports