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 organizations 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 billion 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.
U.S. 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.
NEW ENCASEMENT AT CHERNOBYL
Ministers and officials from the Group of Eight industrial nations and the European Union took the lead at the conference, saying they were ready to fund a new giant encasement over the Chernobyl reactor that exploded in 1986, billowing radiation across Europe.
The plan is to build a 110-meter-high (360-foot) shell over Chernobyl's No. 4 reactor, which blew up after a safety experiment went wrong.
Delegates also expressed solidarity with Tokyo's efforts to control the crisis at Fukushima.
Japan's ambassador told the gathering that "under the challenging circumstances" Tokyo would not be able to pledge additional funds to the Chernobyl effort.
Both Chernobyl and the Fukushima crises showed that "nuclear accidents respect no borders," said U.N. Secretary General Ban Ki-moon.
Yanukovich said the Soviet-era disaster at Chernobyl in 1986 had left Ukraine with a "deep wound which it will have to cope with for many years.
"Neither Ukraine nor the world community has the right to turn back from seeking answers to the questions which Chernobyl has presented us with," he added.
Barroso, describing the pledges as a "very good result," said the European Commission had committed itself to putting up 110 million euros. In all, the EU bloc was providing half the funds required for Chernobyl "shelter and safety" projects.
The European Bank of Reconstruction and Development said it would commit 120 million euros and French Prime Minister Francois Fillon said his country would provide 47 million euros.
The new structure will cover the present makeshift shelter that is now beginning to leak radioactivity from hundreds of tonnes of radioactive material inside.
WEEK OF COMMEMORATIONS
The donors' conference launches a week of commemorations in Ukraine marking the Soviet-era explosion and fire.
A prevailing southeast wind carried a cloud of radioactivity over Belarus and Russia and into parts of northern Europe.
The official immediate death toll from Chernobyl was 31, but many more died of radiation-related sicknesses such as cancer, many of them in neighboring Belarus.
Chernobyl has remained the benchmark for nuclear accidents. On April 12 Japan raised the severity rating at its Fukushima plant to seven, the same level as that of Chernobyl.
Chernobyl's total death toll and long-term health effects remain a subject of intense debate. Yanukovich said on Tuesday: "As a consequence of the accident, millions of people suffered, thousands of them died."
Prypyat, the town closest to the site, is now an eerie ghost town at the center of a largely uninhabited exclusion zone within a radius of 30 km (19 miles).
(Additional reporting by Pavel Polityuk in Kiev and Tabassum Zakaria in Washington; editing by Mark Heinrich)