"It's hard for those Muslims who have to stay in the trenches. They are cold and there is a lot of water in the trenches as it often rains... It's hard to be a Muslim there," he said.
Ismagilov said he did not know how he would celebrate the end of Ramadan, Eid Al Fitr, later this month.
"You are lucky if you can visit a mosque now and you never know how many people will come, or if they will come," he said.
"If there is heavy shelling, we will probably gather in a basement to pray there."
Ismagilov grew up in the city of Donetsk in eastern Ukraine.
Intrigued by his family's Muslim heritage -- which his parents knew little about -- he went to study theology at an Islamic university in Moscow and later became an imam in Donetsk.
While he grew up in a largely Russian-speaking region, he now prefers to speak Ukrainian.
"I think it's disgusting when Russian Muslims support the war", he said.
Russia treats its ethnic minorities, many of them Muslims, as "people of low quality" and "uses them as cannon fodder" in the war, he said.
"It's no secret that most of the dead enemy soldiers are ethnically from Buryatia, Tuva, Dagestan, Tatarstan, Chechnya," he said, naming Russian regions with large numbers of Muslims and Buddhists.
"I'm absolutely sure that many Muslim fighters taking part in combat would like to fast... because in this case they feel even better with Allah's help," the Mufti Suleymanov told AFP.
Dressed in long robes and a white hat, he was elected mufti last November, replacing Ismagilov.
A soldier standing outside the mosque said he was fasting and that most Muslim soldiers do, unless they are on combat missions.
"When you are going right to the very front line, it's permitted not to fast. If it's not hot and you're not tormented with thirst, then you can fast," he said.
