Beleaguered firefighters trying to curb Greece’s worst wildfire season on record battled two major blazes on Friday: one in Evros, home to what an official has called the biggest wildfire the European Union has faced, and the other near Athens, the capital. Greek authorities investigating the causes of the fires arrested dozens of people on suspicion of arson.

“It’s a very difficult summer,” a government spokesman, Pavlos Marinakis, said at a news briefing on Friday, blaming “the explosive mix of climate change” along with arson. He said that 160 people had been arrested across the country on arson charges, 42 of them accused of intentional arson and the remainder accused of setting fires through neglect. “The culprits will face justice,” he said.

The firefighters are focusing on two fires: one near Parnitha National Park, north of the capital, and the other in the northern region of Evros, where at least 19 people have died.

The outlook for Mount Parnitha, where a large fire has been burning since Tuesday, appeared slightly better on Friday morning when winds briefly dropped, a fire service official said, but firefighters were still striving to contain an active blaze west of the forest in the early afternoon. State inspectors started evaluating the damage to land and homes south of the mountain, where the flames had been doused.

A local man accused of setting a series of fires in Avlonas, north of Parnitha, early Thursday will face a prosecutor on Friday, Greece’s police spokeswoman, Constantina Dimoglidou, said.

Firefighting continued for a seventh day in Evros. “The fires in #Alexandroupolis are now the largest #wildfires on record the EU has faced,” Janez Lenarčič, the European commissioner for crisis management, wrote on social media on Thursday, referring to the capital of Evros. He wrote that more than 73,000 hectares, or about 180,000 acres, had burned.

The charred body of a man was discovered on Thursday in a forest near the village of Lefkimmi in Evros, Greece’s fire service said in a statement on Friday.

Efforts were underway to identify another 18 burned bodies, found on Tuesday in Avantas, a few kilometers southwest of Lefkimmi. The dead, who include two children, are believed to have been migrants because the spot where they were found is near the border with Turkey, a popular crossing point, and no locals have been reported missing.

Greece’s Supreme Court prosecutor ordered an investigation on Wednesday into the causes of the fire in Evros, including the possibility that a criminal organization of arsonists was behind it.

Some Evros residents and national far-right politicians have accused migrants of setting the fires, with at least three men taking the law into their hands. The men locked 13 migrants in a windowless trailer on Tuesday, blaming them for the fires as the trailer’s owner streamed the vigilantism live on social media.

On Friday, the three men faced a magistrate on charges of unlawful detention in Alexandroupolis. The migrants were also in court, to answer to charges of attempted arson, manufacture of explosives and illegal entry into the country.

A lawyer representing the owner of the trailer, whom he named as Apostolos Tota, said in a statement on Wednesday that Mr. Tota had conducted a lawful citizen’s arrest and that there had been no abuse in the detention, nor a racist motive.

“He saw a group of illegal immigrants near the incendiary devices trying to light them,” the lawyer, Vasilios Demiris, said, adding that the alleged incident had occurred near his client’s family business in the western outskirts of Alexandroupolis.

A video Mr. Tota posted to social media showed what appeared to be a makeshift incendiary device comprising two car tires, wood and foam. Mr. Demiris said that the charges against the migrants were currently based on the three men’s claims and on the videos but that an investigation was underway to further substantiate the accusations.

The migrants, eight Syrians and five Pakistanis, were expected to be given a 48-hour extension to prepare their defense, one of their lawyers said.