KIEV - World powers, spurred by the nuclear crisis in Japan, pledged 550 million euros ($780 million) on Tuesday to help build a new containment shell at the site of the 1986 Chernobyl accident.

Ukraine had hoped for 740 million euros from governments and international organisations at a conference in Kiev, marking 25 years since the world's worst nuclear accident.

Officials at the conference were optimistic more funds would still be found to make the Chernobyl site safe.

"This is what we have been able to raise through joint efforts - and we consider this figure preliminary - 550 million euros," Ukrainian President Viktor Yanukovich said at the end of the pledging conference.

The world community has already put up a portion of the 1.39 bln euros for the total cost of building a new containment cover and facilities for storing radioactive waste from the reactor.

Though the sums pledged fell short of the 740 million euros still outstanding, European Commission President Jose Manuel Barroso said that when all the pledges were in, it was possible the conference's "very ambitious goal" would be achieved.

China is ready to allocate 4 million euros for the project.

US Secretary of State Hillary Clinton announced $123 million in new funding to help make Chernobyl environmentally safe, on top of $240 million already committed by Washington.

"The completion of two nuclear safety projects, construction of a new safe confinement shelter and a storage facility for spent fuel will help finally close this difficult chapter for the people of Ukraine and the region," she said.