President Barack Obama has ordered a review of US policy on Americans abducted overseas, as intelligence agencies investigate the role of Western jihadists in the beheading of aid worker Peter Kassig.
Washington's refusal to negotiate or pay ransoms contrasts with the stance of several European nations believed to have secretly paid millions of dollars to save abductees, including some held by the Islamic State group.
Kassig was the third American killed by IS, a Sunni Muslim extremist group that has captured large parts of Syria and Iraq, committing widespread atrocities and prompting a wave of US-led air strikes.
The parents of the 26-year-old paid tribute to their son and said they would try to "forgive" the jihadists.
Obama's recently ordered review will focus "on examining family engagement, intelligence collection and diplomatic engagement policies", according to a letter dated November 11 from US Undersecretary of Defence for Policy Christine Wormuth to a Republican lawmaker.
The move comes "as a result of the increased frequency of hostage-taking of Americans overseas, and the recognition of the dynamic threat posed by specific terrorist groups," Wormuth said in the letter, first published by The Daily Beast news site on Monday.
Kassig, who took the name Abdul-Rahman after converting to Islam, was captured last year and became the fifth Western hostage to be beheaded by IS after American journalists James Foley and Steven Sotloff, and British aid workers David Haines and Alan Henning.
Foley's parents defied government advice and began raising funds for a ransom but were told by US officials that they would be forbidden by law from paying.
Sotloff's family also said they were told by a White House counterterrorism official that they could face prosecution if they paid a ransom.
US officials insist Washington's opposition to the practice has deterred groups like Al-Qaeda or IS from taking more Americans hostage.
- 'Forgive and heal' -
The killing of Kassig and the simultaneous beheadings of at least 18 Syrian military personnel in a video posted online on Sunday sparked global horror, with Obama calling it "an act of pure evil".
Kassig's parents called for healing and prayer as they mourned the loss of their son, who took the name Abdul-Rahman after converting to Islam.
"Please allow our small family the time and privacy to mourn, cry and -- yes -- forgive and begin to heal," his father Ed said in an emotional address outside his church.
Signup to our newsletter and follow us on Facebook and Twitter!
Mother Paula said that while their world had been torn apart by the death of their son, they would focus on healing.
"Rather than letting the darkness overwhelm him, he has chosen to believe in the good, in himself and in others... One person makes a difference," she said of her son.
The policy review comes as Washington prepares to double its military personnel in Iraq to up to 3,100 as part of the international campaign it heads against IS.
US Secretary of State John Kerry described the battle against the jihadists as a conflict "between civilisation itself and barbarism."
The extremist group has suffered recent battleground setbacks in Iraq, where government troops on Saturday broke the its months-long siege of the country's largest oil refinery.
- Foreigners at forefront -
Among the militants shown beheading the Syrian servicemen in the latest IS video were some known foreign fighters, including at least one Frenchman and possibly a Briton and other Westerners.
The executioners' faces were uncovered.
French authorities identified one of them as Maxime Hauchard, 22, from a small village in northern France, who left for Syria in August last year.
The Paris prosecutor's office said "circumstantial evidence confirms the involvement of a Frenchman in the decapitation of Syrian prisoners shown in an IS video released on Sunday."
It said it was "possible" a second -- still unidentified -- Frenchmen appeared in the video.
Thousands of foreign fighters have flocked to join IS in Iraq and Syria, and experts say they are often among the most violent and brutal of the jihadists.
A British-accented jihadist has been at the centre of previous IS beheading videos and appeared again in the recording claiming Kassig's killing.
The Syrian Observatory for Human Rights, a Britain-based monitoring group, said it had documented the execution of 1,429 people in Syria by IS in the five months since it declared a "caliphate" in areas under its control.