This post was updated at 2:51 p.m.

Seattle Mayor Mike McGinn on Thursday afternoon vetoed the Seattle City Council's Highway 99 tunnel agreements.

In a statement issued following the veto, McGinn said the action was necessary to "protect Seattle from the unacceptable risks of this project." A spokesman for the mayor said he will speak further about the veto in his State of the City message Tuesday.

The council's 8-1 pro-tunnel majority will likely vote to override the veto Feb. 28.

Council members expressed disappointment at McGinn's veto.

"Ten years of debate is enough. This solution is a critical safety measure for the corridor, while serving as an opportunity for better transit and mobility, bringing economic vitality to the region and creating a waterfront for all," said a statement released by Council President Richard Conlin and Councilmember Tom Rasmussen.

The agreements describe how the City Council and staff would work with the state Department of Transportation on scheduling, utilities and right-of-way issues. The state agreed to defend the city against tunnel-related lawsuits or insurance claims in the event the construction causes property damage. Work might begin by late summer, though two initiative campaigns seek to prevent the project.

McGinn argues that barring a change in state law, city taxpayers would be on the hook for cost overruns on the $2 billion tunnel, part of a $3.1 billion highway project to replace the aging Alaskan Way Viaduct.

Meanwhile, a pro-tunnel political group, "Tunnel + Transit," produced a one-minute video accusing McGinn of flip-flopping on his late-2009 campaign promise not to obstruct the project. Pickus replies that in the same 2009 statement, McGinn said he "will not stop asking the hard questions" to protect Seattle citizens' interests.

A group of pro-tunnel business and community leaders met Wednesday with McGinn to urge him not to veto the City Council's agreements with the state. They reminded him of his campaign pledge to not stand in the way of the tunnel.

In a letter to the mayor, signed by 17 tunnel supporters, the group argued that the council agreements protect the city from cost overruns and ensure the city's participation through planning and construction.

"As this is a state project which could proceed with or without the city's permission or approval, all a veto would accomplish is to take away the protection and guarantees the (Council) Ordinance gives the City -- in our opinion, a veto would not be a good idea."

The letter concludes that the "time has long since passed to second guess the bored tunnel decision" and says the city's best interests would be served by moving forward.

Staff reporter Lynn Thompson contributed to this report.