Silvio Berlusconi has been accused by opponents of spouting "dangerous electoral propaganda" after he vowed to ease the tax burden on austerity-stricken Italians if his rightwing coalition wins elections this month.

With only three weeks to go before the country goes to the polls, the threetime prime minister is gaining ground on centre-left frontrunners in what he described on Sunday as his "last great electoral and political battle". One opinion poll released on Friday had his grouping within five points of the Democratic party-led coalition.

In a speech aimed at winning over the large number of undecided voters, the billionaire media mogul cast himself once again as a friend of the people who would break with the agenda of the technocrat prime minister, Mario Monti.

The centrepiece of a series of measures announced in Milan was a promise not only to abolish the loathed property tax but also to refund payments made in 2012 – costing the treasury an estimated €4bn (£3.5bn).

"This tax caused Italian families worry, anxiety, fear of the future," said Berlusconi, describing the refund as "an act of peace" from the state to the people. A part of the IMU property tax, the levy on first homes, has been highly unpopular ever since Monti imposed it in 2011. Berlusconi has already abolished it once, upon returning to power in 2008.

The 76-year-old, who has said he will be finance minister rather than prime minister if his alliance pulls off an unlikely triumph, also said a rightwing government would abolish, over the course of five years, a regional tax on business. He promised not to increase VAT and said that, "above all", there would be no "wealth tax" on high earners.

The speech was met with a standing ovation from party chiefs and supporters but with stinging criticism from Berlusconi's opponents who accused him of irresponsible electoral trickery that Italy's stagnant and struggling economy cannot afford. The country – in recession for the fourth time since 2001 – has the second highest public debt-to-gross domestic product ratio in the eurozone, behind Greece. Unemployment has risen from 8.4% in 2011 to 11.2% in December.

Monti, whose eclectic group of centrist parties is lagging behind in the polls, said: "Berlusconi governed for so many years and kept none of his promises. Moreover, he created many problems, so much so that he to leave [office] … Italians have good memories."

Rosy Bindi, of the Democratic party, denounced the speech as "dangerous electoral propaganda", while Pier Ferdinando Casini, head of the Union of Christian Democrats (UDC) and a former Berlusconi ally, said the former premier was "a great salesman [who] would be capable of selling anyone a car without a motor".

But the man himself was defiant. "We think we are close to an historic result," he said. "Simply put, we are sure we are going to win."

Berlusconi was forced to stand down as prime minister at the end of 2011 by a combination of personal scandal and economic crisis, and his Freedom People (PDL) party supported Monti's government until December, approving nearly all the technocrats' austerity measures.

But Berlusconi now added that, instead of reviving the Italian economy, tax rises and other measures had merely served to cause unemployment to increase and consumption to fall. He claimed he would cover the revenue lost by the refund with other measures including a reduction of state funding to political parties and a tax, to be agreed with Switzerland, on financial activities by Italian citizens in the neighbouring country.

A SkyTG24-Tecne opinion poll published at the end of last week put Berlusconi's rightwing coalition on 28.7%, just 4.9 points behind Pier Luigi Bersani's centre-left grouping on 33.6%. The same poll had Monti's centrists on 13.8%, beaten into fourth by the comedian-turned-politician Beppe Grillo, whose Five Star Movement was on 15.7%.

• This article was amended on 5 February 2013. The original implied that the IMU property tax is solely the tax on first homes, rather than all property owned by an individual. This has been corrected.