Six months after the Vikings stadium deal paved the way for a public-private renovation of Target Center, the city of Minneapolis and the Timberwolves haven't agreed on how much money the team will contribute to the aging arena.

The implementation committee for what may be a $100 million renovation of Target Center has already met twice. But the city's lead official on the project, Jeremy Hanson Willis, expressed frustration this week that a deal hadn't been inked.

"We've said that we need to have significant private contribution in order for us to do this renovation," Hanson Willis said after a Tuesday meeting of the committee. "And we don't yet have confirmation about to what degree the private sector is going to contribute to this."

The Timberwolves contend that's because the city delayed the process by unexpectedly boosting the private share of the renovation cost from one-third to one-half. That money will come from the team and operating company AEG. The city's publicly stated cost for the project recently fell from $150 million to $100 million, though the Timberwolves haven't agreed to the latter figure.

Ted Johnson, a senior vice president of the Timberwolves, said Wednesday that the team found out from the newspaper last spring that the city wanted a higher proportion of Target Center money to come from the private sector.

"We're dealing with the new ratio that's been put to us," Johnson said. "We have twice stepped up our private commitment from where we started a year and a half ago."

Johnson declined to say where the team's contribution stands, or what the team thinks the arena upgrade will cost. But the team has recently put forward a new funding framework that includes a 50/50 split, he said.

"We haven't agreed upon a $100 million project," Johnson said. "We're still negotiating the project. I think there's still differences of opinion of what the scope of the project should be."

The city has already entered into a $20,000 consulting contract with AECOM, a deal that also includes Mortenson Construction. A timeline, distributed by Mortenson at Tuesday's meeting, projects that construction will begin May 10, 2013.

Hanson Willis said while much of the discussion centers on the total cost of the project, there's also no agreement between the Timberwolves and AEG about how they will divide the private expenses.

"I wish we would have had an agreement by now," Hanson Willis said. "It would have made the work of this committee and a lot of our work easier."

By contrast, the Vikings stadium implementation committee did not start meeting until the payment structure had been settled.

The renovations are needed to improve many facets of the 22-year-old Target Center, which lacks the amenities of its peers in the metro area and the NBA. Behind-the-scenes improvements are also necessary, such as adding loading bays, freight elevators and storage space for bleachers.

AEG's Steve Mattson said he would defer to the city on how to characterize the process, but said he believes the pace has been reasonable. AEG's role is slightly different from the Timberwolves', since the city has hired it to manage the building.

The public portion of the project will be paid with the same funding stream as the city's contribution to the Vikings stadium: sales taxes. Those dollars currently pay debt on the city's convention center, but money will be freed up when the facility's bonds are paid in 2020.

Eric Roper • 612-673-1732 Twitter: @StribRoper