MILAN (Reuters) - Fiat's chief executive has returned to the United States for talks as pressure builds to seal a partnership deal with Chrysler before the end of the month, sources at the Italian car maker said on Monday.

Chief Executive Sergio Marchionne is going to Detroit and Washington, where the government has given Fiat (FIA.MI) and Chrysler CBS.UL an April 30 deadline to get the U.S. car maker's unions and bondholders to agree the deal, the sources told Reuters on condition of anonymity.

Marchionne will not go to Canada, where the Canadian Auto Workers (CAW) union had invited him to take part in their talks with Chrysler, they said.

The union has proven to be more resistant to the deal's terms than its U.S. counterparts. Marchionne has threatened to abandon the deal if they keep resisting. He will return to Italy for a board meeting ahead of publication of Fiat's first-quarter results on Thursday, the sources added. Expectations of an imminent deal have given Fiat's shares a boost in recent sessions. At 0912 GMT, they were up 2.67 percent at 7.87 euros after trading nearly 7 percent higher.

"People are betting that an alliance will be very positive for (Fiat)," one dealer said. The DJ Stoxx auto index .SXAP was down 3.13 percent.

The shares also got a lift from a report on Friday in Automotive News, an industry publication. It said Fiat could also form an alliance with General Motors Corp's (GM.N) operations in Europe and Latin America. Fiat declined to comment on the report.

(Reporting by Gilles Castonguay and Giancarlo Navach in Milan and Gianni Montani in Turin; editing by Simon Jessop)