"The circle of suspects is narrowing. Prosecutors are now receiving information about the poison itself, its chemical features, and the way of its possible application," Yushchenko said in an interview with The Associated Press at the House of Chimeras, a 19th century building decorated with statues of mythical creatures that is used for official functions.
"When it comes to who did it — it was the regime itself. The people in power. No doubt about that," he said. He did not give names, but he has repeatedly noted that he became ill after eating dinner with senior officials of the national security service in September, as his campaign to succeed Kuchma was accelerating.
Yushchenko, a pro-Western reformist, defeated Kremlin-backed Viktor Yanukovych in last year's bitterly contested election. Kuchma had hand-picked Yanukovych as his intended successor.
The poisoning left Yushchenko seriously disfigured, with lesions and discolored skin. In the interview, he appeared tired, but aides said it was the result of a long meeting to work out last-minute details for a trip to the United States that begins Sunday.
The Ukrainian leader will hold talks with President Bush next week at the White House and hopes to repair relations that deteriorated after Washington accused Kuchma's regime of selling radar systems to Iraq in violation of international sanctions.
Although the sale to Iraq has not been definitively proven, Ukrainian officials recently released information about an array of shady weapons deals under Kuchma, including cruise missile sales to Iran and China.
"It was not easy for me and my government to publicly announce facts about such dealings shortly before the trip to the U.S.," Yushchenko said. He said he and Bush will "review all the steps aimed at ending such practices."
"We will also have to think how to formulate the security policies about illicit trade of these types of weapons," he added.
After the radar scandal, Ukraine sent 1,650 troops to Iraq in a move widely seen as an attempt to smooth relations. However, the deployment was widely unpopular at home and Ukraine began withdrawing troops this spring.
Yushchenko said the pullout likely will be completed in the autumn.
"It will be by mid-October, but I don't exclude that this date can be changed a little. But for sure our troops will leave Iraq this year," Yushchenko said at a pre-trip briefing for foreign journalists.
Earlier Thursday, the Defense Ministry said Ukraine will continue to provide weapons and training for Iraq's fledgling security forces in spite of the troop withdrawal.
Yushchenko told the briefing he will aim to return relations with Washington to a friendly and productive level. "We are strategic partners. I want U.S. ministers to know the way to Kiev, to know their Ukrainian counterparts," he said.
"Ukraine has the aim of playing a major role in international policy," Yushchenko said.
Top issues to be discussed on his trip include what role the United States can play in settling the conflict in Trans-Dniester, an ethnic Russian separatist region of Moldova that borders Ukraine, Yushchenko said.
He also said that he wants to liberalize the visa regime with the United States and he said Thursday that he had signed a decree abolishing the requirement for citizens of European Union countries to have visas.
By Aleksandar Vasovic