KYIV, Ukraine (AP) — Ukrainian forces fought off continuing Russian efforts to occupy Mariupol and claimed to have retaken a strategic suburb of Kyiv, mounting a defense so dogged that it is stoking fears Russia’s Vladimir Putin will escalate the war to new heights. The warnings came as attacks continued in and around Kyiv and Mariupol, and people escaped the battered and besieged port city. Explosions and bursts of gunfire shook Kyiv on Tuesday, and black smoke rose from the north. Russian forces also continued their siege of Mariupol after the southern port city’s defenders refused demands to surrender. But the Kremlin’s ground offensive in other parts of the country advanced slowly or not at all, knocked back by lethal hit-and-run attacks by the Ukrainians.