Lawmakers on a U.S. Senate-House committee are making progress on finalizing a transportation spending bill, Senator Barbara Boxer said on Wednesday, although a provision that would fast-track the Keystone XL crude pipeline is still unresolved.

The committee's starting point is a two-year, $106 billion bill to fund road, bridge and rail projects passed by the Senate in March.

Republicans have insisted that the legislation include approval of the Canada-to-Texas Keystone oil pipeline, which President Barack Obama put on hold earlier this year after environmentalists raised concerns.

In a weekly update on the closed-door negotiations on how to advance the bill, Boxer, the Democratic chairman of the Senate-House panel, said she was more optimistic than ever that a deal could be reached by a June deadline after discussing the bill with Republican House Speaker John Boehner on Tuesday evening.

"He (Boehner) is working to make sure we get this done, and that is the best news I have heard in a long time," Boxer said, without addressing specifics of the thorny points of the talks.

"Our conversation was really good. Nobody brought up any quote-unquote 'sticking points.'"

In a statement, Boehner said Keystone remains a priority.