Ukrainian presidential hopeful Viktor Yushchenko returned to campaigning on Saturday in a defiant mood after recovering from what his supporters said was an attempt by authorities to poison him. Opposition leader Yushchenko stopped campaigning for an Oct. 31 poll and flew to Vienna for treatment more than a week ago after being taken ill with what aides said was first thought to be food poisoning but later turned out to be chemical poisoning. "The last two weeks have been the most tragic in my entire life," a pale Yushchenko told 50,000 supporters who gathered on a square in central Kiev. "It could have been that I wouldn't be standing here." "But I want to tell the authorities -- you will not poison us, you will not destroy us," the former prime minister said as supporters chanted his name and waved orange flags, the colour of the opposition. His senior aide Oleksander Zinchenko said on Friday there was enough evidence in the analysis of Yushchenko's medical tests to say there had been an attempt on his life. The office of President Leonid Kuchma dismissed allegations of foul play. Yushchenko is leading in opinion polls by around seven percentage points over Prime Minister Viktor Yanukovich, an ally of the outgoing Kuchma some six weeks before the poll. --more 2306 Local Time 2006 GMT