The Italian president, Giorgio Napolitano, asked the mayor of Florence, Matteo Renzi, to form a new government on Monday – the economically troubled country's third in two years.

If he can pull together a coalition that wins the backing of parliament, Renzi, 39, will become Italy's youngest ever prime minister.

Emerging from a 90-minute discussion with the president, Renzi said he would take a few days to draw up a list of proposed ministers and a programme. "Nevertheless, I assure [you] that I shall put into this task all the energy of which I am capable," he said.

The signs were that votes of confidence in the two chambers would not be held until Friday or Saturday.

Renzi said he intended to concentrate initially on getting a new electoral law for Italy and starting the process of constitutional reform. Over the next three months, he would focus on jobs, the reorganisation of the public sector and, finally, taxes.

Renzi, who leads the centre-left Democratic party (PD), arrived at the palace driving a white Alfa Romeo. The young mayor forced his party colleague, Enrico Letta, to resign as prime minister last week after complaining repeatedly of delays in the government's reform programme.

Letta was hamstrung by a coalition that included the New Centre Right (NCD), a party that broke away from the movement led by Silvio Berlusconi and has different views on a broad range of issues. Renzi, who has no experience of either government or parliament, will also need the NCD's support, however.

Bond and share markets reflected optimism about the proposed new government as they reopened for the week's trading. The gap between Italian and German sovereign interest rates, which narrows when doubts recede about Italy's ability to repay its debts, shrank by five basis points from the Friday close of 200. The Milan bourse opened fractionally higher, consolidating its position as the best-performing leading stock market in Europe so far this year.

Investors appeared to have been buoyed by a decision by the ratings agency Moody's to upgrade its assessment of the outlook for Italian bonds. But they were also thought to be taking into account hopes that Renzi could speed the pace of .