KIEV, UKRAINE - Ukraine is seeking $1 billion to seal Chernobyl, the site of the world's worst nuclear disaster, and concern is mounting that the accident at the Fukushima nuclear plant in Japan and a growing debt crisis may make it harder to raise the money.

Ukrainian President Viktor Yanukovich is hosting a conference in Kiev to get funding for a new containment shelter 25 years after Chernobyl's No. 4 reactor exploded. European Commission President Jose Barroso, who arrived Monday, urged contributions to the venture during an international conference this week.

Japan's battle to contain four damaged reactors at the Fukushima Daiichi nuclear plant has reignited the debate about Chernobyl, whose makeshift shelter has five years left in its lifespan and still leaks radiation. The Ukrainian government warned that aid may fall short as governments cut spending and balk at a fundraising effort that has been going on since 1997.

"The Fukushima disaster definitely gives a renewed sense of urgency for fixing Chernobyl," said Mark Hibbs, a senior nuclear analyst at the Carnegie Endowment in Berlin. "Everybody said that Chernobyl could never happen again."

The conference is part of a week of commemorations centering on the April 26, 1986, meltdown that killed at least 31 plant workers and firefighters in three months and forced the evacuation of a quarter of a million people. The U.S. delegation is being led by Zbigniew Brzezinski, the former national security adviser to President Jimmy Carter.

The meeting, planned before the Japanese earthquake and tsunami damaged the 40-year-old Fukushima plant, has been given new significance, Yanukovich said.

Japan on April 12 raised the severity rating at the stricken Fukushima plant to seven, the same as Chernobyl as radiation leaks continue, and Yanukovich said that solving Chernobyl is an international responsibility.

"To overcome a tragedy of such a large scale cannot be done by one country," he said Monday at the Kiev briefing with Barroso. "Events in Japan showed that such catastrophes are a challenge for all of mankind."

So far $1.43 billion has been collected for the new Chernobyl seal with the European Union and the United States the two biggest donors. An additional $1.05 billion is needed to complete the structure and add spent-fuel storage facilities for the four reactors, said Ukraine Emergency Minister Viktor Baloga.

The project involves a 344-foot high arched roof that, once assembled on a field next to the damaged reactor, will be rolled into place and sealed for 100 years. After that, workers will be able to dismantle the old structure from inside the protective cowl. Work has already begun on pouring the concrete base.