Greta Thunberg was briefly detained by German police at a demonstration over a coal mine expansion along with multiple other demonstrators on Tuesday. Thunberg was carried off by cops and was eventually seen sitting in a police bus alone. However, just a few hours later, the 20-year old Swedish climate activist was let go after her identification was verified, police reportedly told Reuters.

The police claimed all the other protestors would also be released without official arrest or charges, following ID checks, according to Reuters.

Police detained the activists amid ongoing protests against the expansion of an open-pit lignite mine near Lützerath in western Germany. Lignite is known as the dirtiest form of coal. It is a soft, brown fossil fuel—less energy dense than its shiny, black counterpart—and it produces more CO2 emissions and other pollutants per unit energy than gas or any other type of coal. The mine near Lützerath already yields about 25 million metric tons of lignite every year, and German utility RWE is aiming to increase that production capacity.

In order to complete the planned expansion, German authorities granted RWE permission to demolish the small village of Lützerath. The town’s residents were evicted in preparation, and the village had mostly been cleared of occupants by 2017. But then, environmental activists started moving in, in an attempt to occupy the site and slow down or stop the mine’s development.

Police removed almost all of those occupiers last week, some after two years of continual inhabitance in the condemned village, using what many activists described as excessive force. One video showed police charging protestors with batons. (In contrast, another video showed police, decked out head-to-toe in riot gear, struggling to stand upright in thick mud while being taunted and pushed over by a person seemingly in some sort of monk costume.)

And though police stated on Friday, “there are no further activists in the village of Lützerath,” thousands showed up to protests over the weekend, including Thunberg. In an address to the crowd on Saturday, she called the expansion of the mine a “betrayal of present and future generations.”

The German government has previously said it’s aiming to phase out coal as a power source by 2030. RWE agreed to end lignite-based energy generation on the same timeframe. In November, the country’s cabinet approved a draft law to shut down all but two coal-fired power plants in one northwestern German state. But a lack of Russian natural gas resources resulting from the war in Ukraine has thrown a wrench in the country’s planned energy transition, according to German authorities and government officials.

A lignite mine expansion seems entirely counter to the elimination of coal power within seven years, but RWE has claimed the deposits underneath Lützerath are necessary, even for this winter, according to the BBC. “The coal under the former settlement of Lützerath, which is located close to the current edge of the Garzweiler opencast mine, is needed to make optimal use of the lignite fleet during the energy crisis,” the energy company wrote in a press statement.