"Now is the time to focus on God," the husband of slain pastor Myra Thompson, who was murdered in the Charleston church massacre last year, said as the first anniversary of the shooting approaches.

Rev Anthony Thompson on Wednesday led a Bible study on Mark 4:1-20; the same passage his wife was leading from on June 17 last year.

She was one of nine shot dead by suspected gunman Dylann Roof in the basement of the Emanuel AME Church in Charleston, South Carolina.

According to the Charleston Post and Courier, more than 175 people gathered in the church this week to mark the anniversary of the massacre. Anthony Thompson said he had struggled over the past year, but has relied on the Bible to give him strength.

"It can change our attitudes; it can change our hearts to be who God wants us to be, to do what God wants us to do," he said.

In the days and weeks following the shooting last year, Charleston AME Church made headlines as its congregation forgave Roof.

Just two days after the massacre, the relatives of those killed stood up one by one at Roof's bond hearing and offered him their forgiveness.

"You took something very precious from me, but I forgive you," Ethel Lance's daughter, Nadine Collier, told him. "It hurts me. You hurt a lot of people, but may God forgive you."

"We would like you to take this opportunity to repent," said Anthony Thompson Myra Thompson's grandson. "Repent. Confess. Give your life to the one who matters the most, Christ, so he can change your ways no matter what happens to you and you'll be OK."

The following day Cynthia Hurd's husband, Arthur, said: "What I can say to that young man is that in time I will forgive you."

Charleston is known as 'the Holy City' because of its vast number of churches. Emanuel was founded by freed slaves almost half a century before the US formally abolished slavery and is the oldest African Methodist Episcopal church in the Southern United States.

Roof, 21 at the time of the shooting, had written a manifesto online ahead of the shooting, in which he said he had "no choice" but to kill black people.

"I have no choice. I am not in the position to, alone, go into the ghetto and fight. I chose Charleston because it is most historic city in my state, and at one time had the highest ratio of blacks to Whites in the country," he wrote.

"We have no skinheads, no real KKK, no one doing anything but talking on the internet. Well someone has to have the bravery to take it to the real world, and I guess that has to be me."

Roof's death penalty trial is to begin on November 7.