CNN announces that the US has confirmed that ISIS captive Kayla Mueller is dead. Photograph shared by @AdhamEtoom on Twitter

American humanitarian aid worker Kayla Mueller, 26, who has been held hostage by terror group ISIS, has been confirmed dead today. She is fondly remembered in Palestine, where she volunteered with the International Solidarity Movement (ISM) in August and September, 2010, “nonviolently resisting the confiscation and demolitions of the homes and lands” of Palestinians.

The confirmation of her death comes days after the militant group said that she was killed during a coalition airstrike near Raqqa, Syria. Mueller, from Arizona, was captured in August 2013 from Aleppo, Syria, where she was volunteering with Spanish Doctors Without Borders hospital. The ISIS, which has established Raqqa as the capital of their Islamic-styled Caliphate, announced that she had been killed in a Jordanian airstrike, launched in revenge for the murder of Jordanian pilot Muath Al Kasasbeh, who was put in a cage and set on fire last week.

According to CNN, Mueller had “thrown herself into international causes” since she was a teenager. The report explains:

In 2012, Mueller went to Syria with the Danish Refugee Council and Support to Life humanitarian agency.

She fell into the hands of hostage takers in August 2013 in Aleppo, Syria, her family said, after leaving a Doctors Without Borders hospital.

Her family heard nothing until 10 months later, when ISIS got in touch with its ransom demand.

Mueller at a protest tent in Sheikh Jarrah. Photo courtesy of ISM

According to the ISM, Mueller volunteered with them from August to September 2010, where she “worked with Palestinians nonviolently resisting the confiscation and demolitions of their homes and lands.”

In the Sheikh Jarrah neighborhood of Occupied East Jerusalem, she stayed with the Al Kurd family to try and prevent the takeover of their home by Israeli settlers.

While in Palestine:

Kayla accompanied Palestinian children to school in the neighborhood of Tel Ruimeda in Al-Khalil (Hebron) where the children face frequent attacks by the Israeli settlers and military. She stayed with villagers in Izbat Al Tabib in a protest tent to try to prevent the demolition of homes in the village. She joined weekly Friday protests in Palestinian villages against the confiscation of their lands due to Israel’s illegal annexation wall and settlements.

ISM also shares some of Mueller's writings during her work in Palestine:

Kayla published writing online about her work in Palestine with the International Solidarity Movement in August and September 2010. “How can I ignore the blessing of freedom of speech when I know that people I deeply care for can be shot dead for it?” she wrote.

You can read the rest of the posts here.

Online, tributes pour in for Mueller, from around the world.

ABC 15 Arizona shares a letter handwritten by Mueller in the Spring of 2014:

NEW: Here is a letter #KaylaMueller wrote in the Spring of 2014. http://t.co/c5S5Sph6br pic.twitter.com/DCsN69bhzo

— ABC15 Arizona (@abc15) February 10, 2015

In the letter, she writes:

I am not breaking down and I will not give in no matter how long it takes… I know you would want me to remain strong. That is exactly what I am doing. Do not fear for me, continue to pray as will I and by God's will we will be together soon.

Egyptian Mahmood Ali describes the airstrikes as “too stupid,” adding they did not discriminate between jihadists and innocent people:

This proves what we are saying for months.Coalition strikes too stupid it's don't kills jihadist only #KaylaMueller pic.twitter.com/nOlAItQUXR — محمود علي (@maxrx_1987) February 10, 2015

He mourns Mueller with resignation:

#KaylaMueller she was a great person . unfortunately we know who killed her but we can't do anything pic.twitter.com/9syq8ZbrIi

— محمود علي (@maxrx_1987) February 10, 2015

Washington DC-based lawyer Rabia Chaudry adds:

My heart is full of pain for the family/loved ones of #KaylaMueller & for injustice she suffered. May she rest in peace. And ISIS in pieces.

— rabia chaudry (@rabiasquared) February 10, 2015

And Mauritanian-American activist Nasser Weddady concludes:

Kayla, Peter, Steven, Jim #RIP #NeverForget

— weddady (@weddady) February 10, 2015