The head of the World Council of Churches (WCC) sent his condolences on Tuesday to church officials in Russia as the country held a day of mourning for the more than three dozen people killed in a subway by suicide bombers.

"We have received with shock the terrible news of the terrorist attacks in the Moscow Metro," the Rev. Olav Fyske Tveit said in a letter to Patriarch Kirill of Moscow and all Russia.

Expressing his "compassion with all victims and their families," Tveit called the attacks "a sin against God who offers life as a divine gift" and said the attacks "are even more painful…because they were committed during the Holy Week when…all Christians, are reflecting on our Lord Jesus Christ's sufferings for us and our salvation and prepare ourselves to celebrate His Resurrection."

"May God heal the deep wounds caused by these terrorist attacks!" Tveit concluded. "May the Lord of life protect us all from the aggressions of hate and intolerance!"

At least 39 people have been reported dead and over 60 wounded after two female suicide bombers detonated themselves in the Moscow metro on Monday during rush hour.

The attackers are suspected to be part of a larger mob of Chechnyan terrorists known as "black widows," many of whom have lost their husbands or relatives in conflicts with Russians, leaving them with a desire for revenge.

The group, which originally had 30 members, was trained by Islamic militant Said Buryatsky, called "the Russian Bin Laden," who was killed in a sting operation by Russian forces earlier this month.

Authorities are concerned about further attacks from the 19 "black widows" who remain at large.

Russian Prime Minister Vladimir Putin called Monday's attack "a crime with horrible consequences and heinous in nature" and said that he is "confident that the law enforcement agencies will do everything to trace and punish the criminals."

The Russian government declared Tuesday an official day of mourning for the victims of the attack.

U.S. President Barack Obama also sent his condolences saying that "[t]he American people stand united with the people of Russia in opposition to violent extremism and heinous terrorist attacks that demonstrate such disregard for human life."

"My thoughts and prayers go out to those who lost loved ones, and I wish all who sustained injuries a successful recovery," he added.

Meanwhile, officials from the Russian Orthodox Church are urging people not to allow the attacks to deter them from participating in Easter services this Sunday.

 "Love rules at the divine service and perfect love exiles fear," Russian Orthodox Information Department Head Vladimir Legoyda told reporters on Tuesday.

According to Legoyda, "such events shouldn't scare us: if we surrender to fears, we will find ourselves captured by terrorists as thus they will reach their aims both inner and outer."