ATHENS, Greece  — Greek authorities sent 100 extra firefighters Thursday to the country’s northeast where a massive blaze in its 13th day flared up again, prompting authorities to put residents on standby for a possible evacuation for the second night in a row. The fire that started Aug. 19 — part of a busy fire season for Greece — has destroyed vast tracts of forest and burnt homes, and has been blamed for the deaths of 20 migrants whose bodies were found last week in the area, which is near the border with Turkey. Allegations that migrants may have been responsible for the fire have led to some vigilantism against foreigners, though people arrested in recent days suspected of starting blazes around the country have all been Greek. …Greek Prime Minister Kyriakos Mitsotakis defended his government’s response to the fires and said climate change and a protracted heat wave followed by very strong winds were largely to blame for them.