Fiat Chrysler shares fell sharply on Wednesday as analysts questioned whether it could achieve the targets of Chief Executive Sergio Marchionne's new strategy for the carmaker - and how the plan would be funded.

Trading was briefly suspended in Milan after the shares tumbled more than 9 percent. The stock was down 8.4 percent at 7.765 euros as of 9:50 am (1350 GMT), as investors continued to digest the previous day's strategy presentation in Detroit.

Under the plan, outlined in 10 hours of analyst meetings, Marchionne pledged to multiply sales, raise profitability and slash debt by 2018, while investing 48 billion euros ($67 billion) in a global expansion led by the Jeep, Alfa Romeo and Maserati brands.

"These targets were almost unnecessarily bullish, leaving multiple execution challenges - even if they won't be tested for several years," said Citi analyst Philip Watkins.

Quarterly earnings, also published late on Tuesday, were a "major disappointment" that served to underline the challenge, the London-based analyst said in a note.

Fiat Chrysler swung to a 319 million euro net loss in January-March from a 31 million profit a year earlier, missing expectations with a 622 million euro trading profit.

The shares, which had risen 44 percent since Fiat announced a January 1 deal to take full control of Chrysler, opened late in Milan as a result of heavy trading volumes.

"The first quarter was a timely reminder of the risks associated with Fiat's plan," said Exane BNP Paribas analyst Rabih Freiha, citing North American pricing pressure that the brokerage expects to cause more trouble for Chrysler.

The promise to cut debt to 1 billion euros from an expected 11 billion peak next year was "one figure that we believe even the bulls will have trouble justifying", Freiha added.

Marchionne, who vowed to remain at the helm of the company for the duration of the plan, said on Tuesday it represented a new start for the combined group, which has benefited from a strong U.S. market rebound while struggling through Europe's prolonged crisis.

Other analysts suggested the group would eventually have to raise new share capital - a move Marchionne all but ruled out - and had missed an opportunity to do so.

"Fiat's massive plan, and the necessary capital expenditure and R&D, simply do not look affordable or prudent," said Max Warburton of Bernstein Research.

Calling its financial targets "enormously optimistic", Warburton added: "Fiat would do everyone a favour, including its employees, management and shareholders, by raising capital."