A gunman has killed six people and injured at least 14 in a mass shooting in Ukraine's capital before he was shot and killed by police.

Ukraine attacked two Russian refineries and other key oil targets overnight into Saturday, officials said, just hours after the United States granted Moscow another waiver on the sale of its sanctioned oil.

The KN-23s and KN-24s used against Ukraine were made with cheaper parts and required far bigger engines compared to Russian counterparts, Kyiv said.

A gunman who killed at least five people in the streets of Kyiv, Ukraine, Saturday before taking hostages and barricading himself in a nearby supermarket has been shot dead by police, Ukrainian officials said.

Russia has unleashed a massive drone and missile barrage on civilian areas of Ukraine and is stepping up ground attacks along the front.

MOSCOW, April 18 (Reuters) - Ukrainian drones struck a pair of Volga riverside industrial cities, as well as a Baltic Sea port close to St Petersburg that exports petroleum products, Russian local governors said overnight.

Nearly 700 drones and 19 missiles struck cities across the country overnight, killing 16 people, officials said. Ukraine's capital, Kyiv, was among the hardest hit.

April 15 () - Ukraine's Defence Ministry said on Wednesday it was introducing a new model of operations integrating drone warfare with infantry activity and pointed to successes announced by its top

Russia hammered civilian areas of Ukraine with hundreds of drones and dozens of missiles in an attack that stretched for hours from daytime into the night, killing at least 16 people and wounding more than 100 others as terrified residents cowered in their homes,