KYIV, Ukraine (AP) — Ukrainian military forces have successfully established positions on the eastern side of the Dnieper River, according to a new analysis, giving rise to speculation Sunday that the advances could be an early sign of Kyiv’s long-awaited spring counteroffensive.

The Institute for the Study of War, a Washington-based think tank, reported late Saturday that geolocated footage from pro-Kremlin military bloggers indicated that Ukrainian troops had established a foothold near the town of Oleshky, along with “stable supply lines” to their positions.

Analysts widely believe that if Ukraine goes ahead with a spring counteroffensive, a major goal would be to break through the land corridor between Russia and the annexed Crimean Peninsula, which would necessitate crossing the Dnieper River in the country’s south.

Responding to Ukrainian media reports proclaiming that the establishment of such positions indicated the counteroffensive had begun, Natalia Humeniuk, the spokeswoman for Ukraine’s Operational Command South, called for patience.

While neither confirming nor denying the ISW report, she said only that details of military operations in the Dnieper delta couldn’t be disclosed for operational and security reasons.

Speaking on Ukrainian television, Humeniuk added that it was “very difficult work” when “it’s necessary to overcome an obstacle such as the Dnieper, when the front line passes through a wide and powerful river.”

The Kremlin-installed head of the Kherson region, one of four parts of Ukraine that Russia said it was illegally annexing in September, denied on Sunday that Ukrainian forces have established a foothold on the east bank of the Dnieper.

In a Telegram update, Vladimir Saldo said that Russian forces are “in full control” of the area, and speculated that the images referenced by the ISW may have depicted Ukrainian sabotage units that “managed to take a selfie” across the Dnieper before being forced back.

After more than a year since the Russian invasion, recent fighting has become a war of attrition, with neither side able to gain momentum.

But Ukraine has recently received sophisticated weapons from its Western allies, and new troops freshly trained in the West, giving rise to growing anticipation of a counteroffensive.

American-made Patriot missiles arrived in Ukraine last week and military spokesman Yuriy Ihnat said Sunday on Ukrainian television that some have already gone into battlefield service.

The US agreed in October to send the surface-to-air systems, which can target aircraft, cruise missiles and shorter-range ballistic missiles such as those that Russia has used to bombard residential areas and the Ukrainian power grid.

The fiercest battles have been in the eastern Donetsk region, where Russia is struggling to encircle the city of Bakhmut in the face of dogged Ukrainian defense.