KYIV, Oct 20 - Russian and Ukrainian troops appeared Thursday to be girding for a major battle over the strategic southern industrial port city of Kherson, in a region which Russian President Vladimir Putin has illegally annexed and subjected to martial law.

Fighting and evacuations were reported in the Kherson region as Moscow tried to pound the invaded country into submission with more missile and drone attacks on critical infrastructure, The Associated Press reported.

Putin declared martial law in the Kherson, Luhansk, Donetsk and Zaporizhzhia regions on Wednesday in an attempt to assert Russian authority in the annexed areas as he faced battlefield setbacks, a troubled troop mobilization, increasing criticism at home and abroad, and international sanctions.

The unsettled status of the illegally absorbed territory was especially visible in the Kherson region’s capital, where Russian military officials have replaced Kremlin-installed civilian leaders as part of martial law that took effect Thursday to defend against a Ukrainian counteroffensive.

Russian-installed officials have urged residents to evacuate for their safety and to allow the military to build fortifications. Officials said 15,000 residents of an expected 60,000 had been relocated from the city and surrounding areas as of Thursday.

President Volodymyr Zelensky’s office said Thursday that Ukrainian forces mounted 15 attacks on Russian military strongholds in the Kherson region. For its part, Russia’s Defense Ministry spokesman said the Kremlin’s forces repelled Ukrainian attempts to advance with tanks on the Kherson villages of Sukhanove, Nova Kamianka and Chervonyi Yar.

Zelensky said that the Russians have mined the Kakhovka dam and hydroelectric power station about 70 kms (44 miles) from Kherson city, with plans to blow them up in what he called a terrorism act to unleash 18 million cubic meters (4.8 billion gallons) and flood Kherson and dozens of areas where hundreds of thousands of people live. He told the European Council Russia would then blame Ukraine. (ap/ez)