The Russian force assigned to take over Mariupol has left the Ukrainian port city, a senior U.S. defense official told reporters in a briefing Wednesday.

TOPSHOT-UKRAINE-RUSSIA-CONFLICT

The city of Mariupol is shown in an aerial view.

AFP via Getty Images

There are about 2,000 troops and some Chechen fighters in Mariupol, but 10 Russian battalion tactical groups have moved northward, according to a senior U.S. official.

The official said some units that left Mariupol appeared to pause to be refitted near Velyka Novosilka, a town roughly 60 miles northwest of the city and near the edge of Ukraine's Donetsk region, which Russia is seeking to capture.

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The city of Mariupol was taken over by Russia last month. The Associated Press reported Wednesday that around 600 people were killed in an airstrike on a theater that civilians used as a shelter. The city is important to the Russian military because it is located in eastern Ukraine, which is a focus of Russia's invasion.

Russian forces could move from Mariupol to other parts of the region. According to the Institute for the Study of War, many of these units were damaged in the fighting. The organization said two weeks ago that Russian battalion tactical groups in Mariupol are degraded and unlikely to have their full complement of personnel.