The South Carolina governor has declared that the Confederate flag should be removed from the grounds of the state's main government building.
She acknowledged that its use as a symbol of hatred by the man accused of killing nine black church members has made it too divisive to display in such a public space.
Republican governor Nikki Haley's about-face comes just days after authorities charged Dylann Storm Roof, 21, with murder.
The young white man appeared in photos waving Confederate flags and burning or desecrating US flags, and purportedly wrote of fomenting racial violence. Survivors told police he hurled racial insults during last Wednesday's attack.
"The murderer now locked up in Charleston said he hoped his actions would start a race war. We have an opportunity to show that not only was he wrong, but that just the opposite is happening," she said, flanked by Democrats and Republicans, blacks and whites who joined her call.
"My hope is that by removing a symbol that divides us, we can move our state forward in harmony, and we can honour the nine blessed souls who are now in Heaven," Ms Haley said.
Last week's massacre inside a historic black church has suddenly made removing the flag - long thought politically impossible in South Carolina - the go-to position, even for conservative Republican politicians.
With heavy security and heightened expectations, a crowd began to gather today in the sweltering summer heat to demand the removal of the Confederate battle flag from atop a 30-foot pole outside South Carolina's Statehouse, which houses the governor's office and the local legislature.
"The governor and members of the leadership of South Carolina made a great step forward by indicating that the flag should come down," said Malcolm Graham, a former North Carolina state senator and the brother of one of the shooting victims.
"Whether it comes down today, tomorrow or next week, it's important that there's one flag that all citizens of South Carolina are governed by."
The Confederate battle flag represented the southern states that in 1861-65 tried to secede during the US civil war, which erupted because northern states wanted to abolish slavery and southern states wanted to keep it.
Since then, the flag has turned into a divisive symbol, representing racism to many, southern pride to others.
Ms Haley's declarations sparked action in other arenas as well on Monday: a senior Mississippi legislator called for the Confederate emblem to be removed from the state flag, becoming the first top-tier Republican to do so.
The Democratic governor of Virginia ordered the replacement of vanity license plates depicting the Confederate flag, saying the banner is "hurtful" to too many people.
In Tennessee, both Democrats and Republicans called for the removal of a bust of Confederate general and early Ku Klux Klan leader Nathan Bedford Forrest from an alcove outside the Senate's chambers.
And retail giant Wal-Mart announced yesterday that it is removing any items from its store shelves and website that feature the Confederate flag.
Ms Haley urged the state's Republican-led legislature to debate the issue no later than this summer. If not, she said she will call a special session and force them to resolve it.
Lawmakers have proposed moving the flag to the state-run Confederate Relic Room and Military Museum.
Making any changes to the banner requires a two-thirds super majority in both chambers under the terms of the 2000 deal that moved a square version of the flag to a monument to Confederate soldiers out front.
The last South Carolina governor who called for the flag's removal was hounded out of office in 1998 by a group that represents the descendants of Confederate veterans, effectively ending his political career.