Former Ohio state senator Nina Turner, a prominent figure in Bernie Sanders' presidential campaign, has declined the offer to run as the Green Party's vice presidential candidate because she said she wants to continue to fight for progressive ideals within the Democratic Party.

"I'm going to keep fighting in the party, even though I'm disappointed," Turner said in a telephone interview with Cleveland.com. "I'm a Democrat, and that's worth fighting for."

Jill Stein, the presumptive Green Party presidential nominee, had reportedly offered Turner the position over the weekend after the rising star was barred from speaking at the Democratic National Convention. Last fall, Turner, a vocal critic of the establishment, left a top post within the Ohio Democratic Party to campaign for Sanders.

Speaking to reporters on Monday, Turner said she is going to focus her energy on advancing the progressive agenda put forth by the Sanders campaign. "What I really care about is making this progressive agenda more actionable," she said.

The Green Party announced later Monday that veteran human rights activist and organizer Ajamu Baraka will be joining Stein on the ticket.

Hailing Baraka's "lifelong commitment to building true political revolution," Stein said that he would serve as "a powerful, eloquent spokesperson for the transformative, radical agenda whose time has come—an agenda of economic, social, racial, gender, climate, indigenous and immigrant justice."

Currently serving as an associate fellow at the Institute for Policy Studies, Baraka is also an editor and columnist for Black Agenda Report, has contributed to Common Dreams, and was the founding executive director of the US Human Rights Network.

"Ajamu’s life’s work has embodied the immortal words of Dr. Martin Luther King: Injustice anywhere is a threat to justice everywhere," Stein continued. "In this hour of unprecedented crisis, we are honored to lift up a unified movement for justice in the only national political party that is not held hostage by corporate money, lobbyists and super-PACs. We look forward to bringing this agenda for justice to the American people in the exciting race ahead."

The announcement was made three days before the Green Party's national convention kicks off in Houston, Texas, where the formal nomination will occur.