Karzai also extended his appeal to Taliban fighters based in Pakistan, where many of them fled following the 2001 US-led invasion of Afghanistan.
Concerns that Taliban fighters will attack the polling stations and prevent Afghans from voting - especially in the southern areas of the country - have grown as the Taliban regains control of parts of Afghanistan.
While the Taliban and other fighters have not announced direct plans to target polls, they have told Afghans to boycott the elections.
Two of the more than 3,000 candidates for the provincial councils have been murdered in recent weeks.
The US and other allies have pledged thousands of extra soldiers to protect polling stations and are bankrolling the elections at a cost of $220m.
Last week, Nato's senior military commander warned that fighters could block transport routes and use intimidation to interfere with the elections.
"I'm sure there will be attempts by the insurgents, the Taliban, to interfere with the polling," John Craddock, Nato's supreme allied commander in Europe, said at his headquarters in Belgium.
Karzai urged fighters to contribute to leading the country towards stability through elections and called on candidates to prioritise national unity.
"We can try for peace through elections, and through elections we can bring development to this country," he said.
Karzai also warned against "interference" by any country, which he said might want to influence the outcome of the elections.