Prime Minister Benjamin Netanyahu attributed the fires to “natural and unnatural” causes and said that “any fire caused by arson or incitement to arson is terrorism in every sense of the word, and we will treat it as such.”

Arab leaders in Israel protested the widespread allegations that Palestinian nationalists were behind many of the fires, saying their land was burning, too, and they condemned what they viewed as unfair accusations against Israel’s Arab citizens, who make up about a fifth of the population. Ahmad Tibi, a veteran Arab lawmaker in the Israeli Parliament, wrote on Twitter: “I called Yona Yahav. Our homes are open to the evacuees. Sad and painful. Let’s join hands to overcome the fire and let’s also douse the flames of incitement.”

Mr. Netanyahu spoke on Thursday with President Vladimir V. Putin of Russia, who promised to send two huge firefighting aircraft.

Firefighting planes and teams from Cyprus and Greece had already arrived, and the Israeli police and Foreign Ministry said that more help was on the way from Croatia, Italy and Turkey. The Palestinian Authority also sent some fire engines to tackle the fires.

The Israeli emergency services are more prepared and better equipped than they were in 2010, when a fierce fire raged through the Carmel Forest area near Haifa. More than 40 people, most of them officer cadets from the prison service, were killed in that blaze when their bus was engulfed in flames as they were on their way to evacuate a prison.