The troops arrived by Black Hawk helicopter and targeted areas that Russia claims to hold, Ukraine’s defense forces confirmed to Kyiv Post.
From: Kyiv Post by Alisa Orlova, Kateryna Zakharchenko

Several groups of Ukraine’s Military Intelligence (HUR) special forces landed in the eastern city of Pokrovsk earlier this week in a daring operation overseen by chief Kyrylo Budanov, Ukraine’s defense forces confirmed to the Kyiv Post.
The troops arrived by Black Hawk helicopter and targeted areas that Russia claims to hold.
“Yes, a landing operation took place. Several groups using US-made Black Hawk helicopters landed and entered districts Russia claimed to control,” a source in Ukraine’s defense forces said.
The mission aimed to stabilize the front line and restore vital supply lines cut off by Russian advance, the source said, confirming reports first published by Reuters on Friday about a Ukrainian special forces landing in the city.