Green Party Leader Elizabeth May has denied she told supporters in swing ridings to strategically vote for the Liberals or the NDP as a way to defeat the Conservatives in Tuesday's election.

While May conceded she was apprehensive about vote-splitting in some ridings, she said her supporters should not switch their vote.

"Being honest with the voters, I acknowledge that there is concern over vote-splitting in a small number of ridings. But I am not going to say 'vote Liberal here, vote NDP there,'" May said in a release Sunday evening.

However, earlier on Sunday, May told The Canadian Press that Green Party supporters in ridings where races were closest should vote for other parties in order to block the Conservatives from winning.

"There's no question that there are some ridings where you might say, 'to vote green you ought to vote NDP to stop a Conservative from winning,' and in some ridings 'you might want to vote Liberal to stop a Conservative from winning,'" May said while in Stellarton, N.S.

"It would be maybe 20 per cent of ridings in the country where that's even a factor, and mostly in Ontario."

May's apparent about-face comes as Green voters face increased pressure to switch their votes to beat the Tories, who have enjoyed late-campaign momentum according to some polls.

On Saturday, three Nobel prize-winning scientists - Andrew Weaver from the University of Victoria, William Peltier from the University of Toronto and Carleton University's John Stone - urged May in a press release to advocate strategic votes in close ridings.

Liberal Leader Stephan Dion has further ratcheted up that pressure in recent days by telling Greens to vote for him since he's the only leader who can realistically defeat the Conservatives and adopt greener policies.

Dion will ramp up his "Go green, vote red" pitch on a final, frantic tour across the country to shore up support.

Some polls show that the Liberals trail the Conservatives by about 10 points - a gap that could be closed if Green supporters, who hover at around 9 per cent, rush to support the Liberals.

Meanwhile, May said she wouldn't parachute into a riding won by a Green candidate should she fail to unseat Conservative rival Peter MacKay.

Speaking Sunday on CTV's Question Period, May listed about a half dozen ridings she feels Green candidates have a good chance of winning, including Guelph, Vancouver Centre, Bruce-Grey-Owen Sound and Nanaimo-Alberni.

"We'll have a lot of MPs and I'm not going to ask them to surrender their seats," May said.

May said she is confident she can win in the Central Nova riding held by MacKay for more than 10 years, despite polls that put MacKay ahead by about seven points.