Mattarella rejected Conte's list of potential ministers due to the candidacy of Paolo Savona, who was proposed as a candidate for minister of economy.
"We may now be in for an extended period of heightened uncertainty ahead of fresh elections - assuming that's where we're headed - but that's not a story for today", said Ray Attrill, head of foreign-exchange strategy at National Australia Bank in Sydney.
On Friday, the closely watched gap between the Italian and German 10-year bond yields, seen as a measure of political risk for the euro zone, was at its widest in four years at 215 basis points.
Italy has been without a government since elections in March because no political group can form a majority. Britain's FTSE 100 .FTSE was closed for a holiday and with USA markets also closed, trading volumes were thinner.
After the coalition's collapse, Italian bonds, stocks and the euro rallied. The MIB stock index in Milan was one of the best performing global asset classes in 2017.
Hawaii's Kilauea volcano spews lava
Joe Kekedi takes pictures as lava enters the ocean, generating plumes of steam near Pahoa, Hawaii . Scientists say it can trigger explosions if ignited while trapped underground.
Newspaper La Stampa reported earlier that Conte, a law professor at Florence University with no political experience, will try to persuade and reassure Mattarella that Savona won't seek a euro-exit or create problems with Brussels.
Mattarella's claims that Savona is a danger to Italy's stay in the eurozone lack any ground, Stefano argued, since Savona's current stance is that Italy can assert its place in European economics without necessarily abandoning the euro.
"Membership of the euro is a fundamental choice for the future of our country and our young people", he said.
"Why don't we just say that in this country it's pointless that we vote, as the ratings agencies, financial lobbies decide the governments".
"The market seems to cheer the news, but I don't share the idea that a caretaker government is that reassuring", Stephane Ekolo, equity strategist at TFS Derivatives, says by phone.
Judge: Trump Blocking Twitter Accounts Violates 1st Amendment
Ken Paulson, president of the Freedom Forum Institute's First Amendment Center, said he was surprised by the ruling. She said she assumed Trump's social media director Dan Scavino would unblock the users in light of her decision.
However, any new government has to receive the approval of the Italian parliament.
If Mattarella fails to get the support of parliament, the time-frame for follow-up elections will be pushed forward to the coming months.
Following a general election in early March, the two parties with the most votes-the populist 5Star Movement and far-right League-slowly worked out the terms of a coalition.
The president of Italy, an institutionally respected figure, has limited powers but ones which have often proved crucial during political crises.
The euro gained ground on the news, adding 0.4 percent against the US dollar on Monday morning and ticking up against most other major trading partners as well.
Kilauea volcano glow captured on time-lapse camera
Officials are concerned that " laze ", a risky product produced when hot lava hits cool ocean water, will affect residents. Authorities are urging people to stay away from areas where lava meets the ocean because of its hazards.