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.

CEO Sergio Marchionne is going to Detroit and Washington, where the government has given Fiat and Chrysler an April 30 deadline to get the US car maker's unions and bondholders to agree the deal, the sources said.

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