President-elect Barack Obama has a historic opportunity to drastically reduce the threat of nuclear terrorism and should appoint a senior White House official to take charge of countering the danger, according to a report released Tuesday. Despite progress on improved security, major gaps remain, said the report prepared by Matthew Bunn, associate professor of public policy at Harvard University's Kennedy School of Government. The world still faces a "very real" risk that terrorists could get a nuclear bomb and the incoming president must make reducing the threat a top priority of US security and diplomacy, the report said. "Despite all the challenges he faces, President-elect Obama cannot afford to let this sit on a back-burner," Bunn said in a telephone interview. "It will take sustained White House leadership to close the dangerous gaps that still remain in our efforts to keep nuclear bombs out of terrorists hands," he said. The study found that US-sponsored security upgrades have been completed for about 75 percent of the buildings in the former Soviet Union that contain nuclear material that could be used to make weapons and for roughly 65 percent of Russia's nuclear warhead sites. But there is chronic underinvestment in nuclear security there and insider theft and corruption are major issues that remain. The report cited, for instance, the arrest of a Russian colonel earlier this year for soliciting bribes to overlook violations of nuclear security rules. Among alarming incidents around the world, the report cited an armed break-in at a South African site with hundreds of kilograms of highly enriched uranium and increasing terrorist threats in Pakistan. The proposed senior White House official would have direct access to Obama and take full-time charge of all efforts focused on preventing nuclear terrorism. Other recommendations include launching a campaign to ensure that every nuclear warhead and every kilogram of plutonium and highly enriched uranium are protected against terrorists and criminals. Also, efforts to remove nuclear material from as many locations around the world as possible would be expanded and accelerated. And, the report said, the new administration should ask Congress for about $500 million for a flexible fund to seize opportunities to counter nuclear terrorism.