BBC News with David Austin.

As leaders from nearly 50 countries meet in Washington for a major summit on Nuclear Security, Ukraine has pledged to

eliminate

stockpile of highly enriched uranium by 2012. Ukraine will also

convert

its several nuclear research facilities to use low enriched uranium. The summit, the biggest international meeting hosted by the US since 1945, has been called by president Obama. Our diplomatic correspondent Jonathan Marcus reports from Washington.

The timing may have been

choreograph

ed for the decision by the Ukraine authorities is just the sort of news president Barack Obama wants to hear.

This summit is all about securing stocks of fissile material, highly enriched uranium and plutonium could potentially be used by terrorists to build a nuclear bomb. US officials said that Ukraine has

sufficient

highly enriched uranium for several nuclear weapons. This will be removed with some help from the United States. This is a

precedent

Obama would like other countries to follow and just to underscore the gravity of the potential threat. John Briton, a senior US counter-terrorism official, has warned that al-Qaeda has been seeking material for a nuclear bomb for over 15 years and that interest remains strong.

The body of the Polish president’s wife has now been identified following Saturday’s plane crash in Russia, in which she, her husband Lech Kaczynski, and dozens of senior Polish political and military officials were killed.