An oil spill which has been blamed on a Russian attack in Ukraine has polluted a major river in Moldova, prompting authorities to cut water supplies to the northern city of Balti. Ukrainian authorities said oil began leaking after a Russian strike on the Dniester hydroelectric plant on 7 March, with the first slicks appearing three days later on the Dniester river - a vital source for most of Moldova and the Odesa region in southwestern Ukraine. Moldova imposed a 15-day state of alert in the Dniester river basin on Monday as a precaution. Russia's ambassador was summoned by the foreign ministry in protest and shown a bottle of cloudy water from the polluted river. He refused to comment to reporters as he left the meeting, according to Moldovan media. Moldovan Environment Minister Gheorghe Hajder stated that supplies would only be restored once oil levels are brought down to the recommended limit of 0.1mg per litre of water. Current readings are too high for northern areas including Balti, and further tests will determine if the water can be restored. Three other northern towns are also facing a water crisis. The pollution has reached areas of Ukraine, affecting water supplies in Chernivtsi, Vinnytsya, and Odesa regions, according to Ukrainian Deputy Minister Iryna Ovcharenko. Schools in Balti have shifted to online learning while authorities focus on delivering drinkable water to residents. Moldova's president, Maia Sandu, has expressed strong support for Ukraine and blamed Russia for the pollution crisis.