(CNN) -- Arsonists attacked the administrative offices of leading Israeli football club Beitar Jerusalem on Friday, police said. The attack occurred just days after the club signed two Muslim players.
No one was injured in the fire, which was discovered around 5 a.m., police said. But the blaze damaged the club's trophy room.
Last Thursday, four club supporters were arrested on charges of making racist chants, apparently directed at the Beitar's newest players, Zaur Sadaev and Dzhabrail Kadaev. They came from Russian League club Terek Grozny, based in Chechnya.
On the same day they were signed, January 26, fans at a Beitar match waved a banner reading "Beitar -- pure forever" and chanted anti-Arab slogans. Four were arrested.
The Israeli Football Association later fined Beitar $15,000 and ordered the club to close the area at the Teddy Kollek Stadium where the club's hardcore supporters usually gather.
Meanwhile, investigators continue to figure out who is behind the arson attack.
"A thorough investigation has been opened by a Special Investigations Unit searching for suspects that fled the scene," police spokesman Micky Rosenfeld said.
Israeli Prime Minister Benjamin Netanyahu condemned the "shameful" arson attack in a statement issued Friday.
"We cannot accept such racist behavior," he said.
Beitar's general manager, Itzik Kornfein, issued a defiant message, saying the club would stand by its signing of Sadaev and Kadaev.
He said bringing them on was the "right decision," despite the subsequent controversy.
"We will keep strong," he told CNN.
"The club won't change it's mind because of these criminals," he said. "But I want to emphasize that a minority of people have been causing these actions. Beitar and most of its fans are not racist."
Rosenfeld said security will be stepped up ahead of Beitar's home match Sunday in the Israeli League against Bnei Sachnin, an Arab-Israeli team.
Beitar, owned by Russian-Israeli Arkady Gaydamak, was founded in 1948.
The club's crest features the menorah, which is also embedded in the emblem of the state of Israel.
Throughout the club's history many of their fans have remained implacably opposed to the signing of Arab or Muslim players.