Hillary Clinton on Monday announced the launch of Onward Together, a new political group aimed at advancing progressive causes by harnessing grass-roots opposition to President Trump's policies.

Mrs. Clinton, 69, who until recently had maintained a low profile after her loss in the presidential election in November, said on Twitter that her new group would encourage people to "get involved, organize, and even run for office."

We're launching Onward Together to encourage people to get involved, organize, and even run for office. https://t.co/8exooosvZ5

— Hillary Clinton (@HillaryClinton) May 15, 2017

"More than ever, I believe citizen engagement is vital to our democracy," she added. "I'm so inspired by everyone stepping up to organize and lead."

Mrs. Clinton went on to praise the work of several grass-roots groups that have emerged as part of a broad liberal movement opposed to Mr. Trump and his policies. Onward Together will support those groups, she said, though she did not describe what form the assistance would take.

Onward Together is registered as a 501(c)(4) group, the Internal Revenue Service designation for so-called social welfare nonprofits, which are often cited for a rise in dark money in politics because of their ability to protect donor anonymity.

Mrs. Clinton said that Howard Dean, who has been a presidential candidate, the Vermont governor and chairman of the Democratic National Committee, would be involved, though she did not describe what role he would play.

According to a mission statement posted on its website, Onward Together aims to "advance progressive values" by encouraging political engagement.

"There's no telling what we can achieve if we approach the fights ahead with the passion and determination we feel today, and bring that energy into 2017, 2018, 2020 and beyond," the statement says.

The Indivisible Project, one of the groups that Mrs. Clinton praised, said it did not plan to receive financial support from Onward Together, but greeted the announcement with gratitude.

"We are so grateful for her assistance in amplifying our reach," the organization, a network of more than 5,800 local groups, said on Twitter.

The Republican Party criticized Mrs. Clinton's new group, describing it as simply her old campaign under a new banner.

If at first you don't succeed, repurpose your failed branding. pic.twitter.com/hC3CsZ766J

• — GOP (@GOP) May 15, 2017