Work on the new tracks was halted by the row over extra money
The contractor at the centre of the dispute over Edinburgh's tram scheme has blamed late design changes for escalating costs.
German firm Bilfinger Berger also denied demanding £80m in extra payments before starting work in Princes Street.
The city's main thoroughfare remained closed to traffic despite the suspension of construction.
The company said the main reason was a delay in the diversion of utilities, which is needed before work can start.
The organisation set up by the council to oversee the project, Tie, has accused the contractors of demanding additional payments that could add £50m-£80m to the cost of the project.
But Bilfinger Berger insisted it was acting in accordance with its contract by refusing to start work before utilities such as gas and water supplies had been moved.
A spokesman for the company said these delays would result in extra costs. He also claimed there had been late changes in design.
"There is still no final design of the project on the table," he said.
"If there is a delay, there is extra cost. Our calculation is that we build this now. Where there is a delay in the scope of the work, costs go up."
Talks continued on Wednesday to try to find a resolution to the dispute.
Tie confirmed that there had been delays in utility diversion at Leith Walk and the Gogarburn depot, but insisted this should not have prevented the contractors working.
A source close to the project said: "If you add all the bits together, there's still a lot of space that can be worked on.
"The project involves laying 16km of track. There's about 400m of Princes Street that can be worked on."
The source denied that late design changes would lead to significant extra costs.
They said: "Like all large designs, there are project changes. Compared to other large construction projects the number of design changes has been relatively small."