Story highlights "I saw dozens of people lying on the ground covered in blood," a witness says

At least 40 people have been killed in the suicide blast, a spokesman says

The death toll is likely to climb given the size and timing of the blast, he says

The explosion occurred as worshipers were leaving morning prayers

It was supposed to be a day of happiness, a moment to mark the start of a Muslim holiday that celebrates peace as the faithful observe the height of the Hajj, the annual pilgrimage to Mecca.

It was that kind of day that Zain-ul-Obdin said was needed by the people in Afghanistan's Faryab province, where suicide bombings and insurgent attacks have taken their toll on the population.

The people did not get that day.

It was erased by a suicide bomber who left bodies broken and bloodied outside Eid Gah Mosque in the provincial city of Maimana.

"I saw dozens of people lying on the ground covered in blood," Zain-ul-Obdin said. Among them were the bodies of children, he said.

At least 40 people were killed and more than 50 wounded in the attack that came as worshipers were leaving Friday morning prayers marking the beginning of Eid al-Adha , Lal Mohammad Ahmadzai, a spokesman for the northern Afghanistan police chief, told CNN.

The death toll was likely to rise given the size and timing of the explosion, said Ministry of Interior spokesman Sediq Seddiqi.

There was no immediate claim of responsibility, but Seddiqi laid the blame for the attack squarely at the feet of Taliban leader Mullah Omar.

"Their target and their main objective is to attack and kill as many people as possible," he said.

Eid al-Adha, also known as Feast of Sacrifice, is considered a joyous holiday for Muslims. It commemorates when God appeared to Abraham -- known as Ibrahim to Muslims -- in a dream and asked him to sacrifice his son as an act of obedience.

The mosque had been so packed that Zain-ul-Obdin and his neighbors were forced to pray just beyond the front doors of the mosque.

It was this misfortune at being unable to get into the mosque that may have saved his life.

When the sermon was over, he was among the first to leave the grounds, he said.

At the same time, the bomber -- said to be dressed in a police uniform -- waded into the crowd leaving the mosque and detonated his explosives.

Coming at the start of the Eid holiday, the attack drew swift condemnation from neighboring Pakistan as well as the United States.

"This violence undertaken at a place of worship, and during Eid, once again shows the insurgency's callous hypocrisy and disregard for religion and faith," said Marine Gen. John Allen, commander of the International Security Assistance Force.

Pakistan's Foreign Ministry vowed to stand by Afghanistan in the fight on terrorism.

The U.S. Embassy in Kabul said the attack demonstrated "the insurgency's lack of respect for religion, faith and its disregard for the safety and security of the Afghan people."