A four-year-old Israeli-American girl who was kidnapped by Hamas during its 7 October attack in southern Israel was among the 17 hostages released by the group on Sunday.

Avigail Idan was just three at the time she was taken hostage from her home, where her parents were attacked and killed by Hamas gunmen.

She turned four while she was held hostage by Hamas.

Avigail's family said: "We hoped and prayed today would come."

"There are no words to express our relief and gratitude that Avigail is safe and coming home," said Liz Hirsh Naftali, Avigail's great aunt, and Noa Naftali, her cousin, in a statement.

They also thanked US president Joe Biden, the Qatari government and others who were involved in securing Avigail's release and called for the remaining hostages to be released.

"We have to keep pushing. We will continue to stand with the families of all the hostages still held captive, and we remain committed as ever to securing their safe and swift return."

Earlier, President Biden said Avigail had been through a "terrible trauma", adding what she "endured is unthinkable".

Speaking to reporters, he said those around Avigail will be surrounding her with "love and care."

"Today she's free, and Jilly [first lady of the US Jill Biden] and I, together with so many Americans, are praying for the fact that she is going to be alright," he said.

President Biden said Sunday's hostage releases were the result of "intensive US diplomacy", adding he was hopeful that more American hostages will be released in the coming days.

"We continue to press and expect that additional Americans will be released as well," he said, adding "we will not stop working until every hostage is returned to their loved ones".

Fourteen of the 17 hostages were Israeli and three of them were Thai nationals. Nine of the Israelis were children.

Avigail was in the Kfar Aza kibbutz on 7 October and ran from the house she was in during the attacks.

She was taken in by her neighbours, the Brodutch family, but they were also abducted by Hamas.

Some members of the Brodutch family were among the hostages released on Sunday, including four-year-old Oria, his eight-year-old brother Yuval and their 10-year-old sister Ofri.

Their mother, 40-year-old Hagar Brodutch was also released.

Hagar's father-in-law, Shmuel Brodutch, told Israel's Channel 13 News: "The moment I heard they were in the hands of the Red Cross, I was relieved."

He added: "I hope I can invest the same effort until the last captive returns. I am very happy, but I feel a great commitment to the other families until the last captive returns, including IDF soldiers."

The other released hostages include Chen Almog-Goldstein, 48, and her children Tal, eight, Gal, 11, and Agam, 17, who were abducted from their homes in Kfar Aza on the day of the attack. Chen's husband, Nadav, and their 20-year-old daughter, Yam, were killed by Hamas.

Also released were sisters Dafna and Ela Elyakim, aged 15 and eight respectively. They were taken from their home in Kibbutz Nir Oz on the day of the attack, and were part of a family group whose capture was live-streamed by the attackers themselves.

Their mother, Maayan Zin, said in a statement that she was happy her daughters had returned, adding that it was "a joy mixed with sadness".

"Joy for my daughters who are here and sadness for those who have not yet returned. My heart will not be whole again until everyone returns home safely."

She said that since the girls were kidnapped, she had been living "between despair and hope, between pain and optimism".

"The girls are returning to a new and complex situation, and now we have a period of recovery that will take time," she said.

The other hostages released were 25-year-old Roni Krivoi - a dual Israeli-Russian national, working as a sound engineer at the Supernova musica festival, 62-year-old Adrienne Aviva Seigel who was taken from her home in Kfar Aza along with her 64-year-old husband Keith.

IDF Spokesman Rear Adm. Daniel Hagari confirmed that 84-year-old Elma Avraham was airlifted to Soroka hospital in Beersheba in a serious condition.

Israel's prison service meanwhile has confirmed the release of 39 Palestinian prisoners as part of the four-day truce between Hamas and Israel.

Hamas' attack on 7 October killed 1,200 people, and about 240 were taken hostage.

Since then, Gaza's Hamas-run health ministry says more than 14,500 people have been killed in Israel's retaliatory campaign in the territory.

Sunday marks the third day of a four-day pause in fighting in Gaza during which some of those being held hostage by Hamas are being freed in return for the release of Palestinian prisoners.

The total number of hostages released during the window now stands at 54 and the number of prisoners freed is 117. (BBC)

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