One bomb at a time, the Russians cut electricity, water, food supplies and finally, crucially, the cell phone, radio and television towers. The few other journalists in the city got out before the last connections were gone and a full blockade settled in.
Article source: https://www.huffingtonpost.co.uk/entry/mariupol-siege-ap-journalists-russian-hit-list_uk_6238e955e4b0c727d481cbc2