The killing of two opponents of President Bashar Assad's regime has left their family and the wider relocated Syrian opposition community reeling in shock and fearing for their lives.

Police discovered the bodies of Orouba Barakat, 60, and her daughter, Halla, 23, who is a U.S. citizen, on Thursday night in their Istanbul apartment, reportedly after friends and colleagues were unable to reach them for several days.

Orouba was a member of the Syrian National Coalition, the political opposition group that has participated in internationally brokered peace talks to bring an end to the Syrian war.

Her daughter, Halla, who spent her childhood in Raleigh, N.C., was a journalist who worked with opposition station Orient TV.

Even on her personal Facebook page, the younger Barakat documented the violence taking place in her country, with posts about children killed in airstrikes and photos of victims of mass killings.

Turkish media outlets, citing police sources, reported that the women had been repeatedly stabbed. There were also other, unconfirmed reports that their throats had been slit.

Politically motivated killing?

A police investigation is underway, and as of Saturday, there have not been any official statements about circumstances of their deaths or any suspects.

But relatives and opposition activists immediately characterized this as a politically motivated killing.

Shaza Barakat, Orouba's sister, said Saturday that she suspected the Syrian government is to blame.

"Because Hafez al-Assad had been displacing us since the 1970s," she told NPR, referring to the former Syrian president and father to Bashar Assad. "We paid a high price — displacement, torture, suffering — we don't have a country."

"Orouba was always standing against all that, defending people's rights and demanding justice. We are people, we have human rights, and we deserve justice."

In an earlier post on Facebook mourning her sister, Shaza wrote: "The oppressor chases the good everywhere."

Ghassan Aboud, the founder of Orient TV, wrote on Facebook: "No truce and no reconciliation with the monsters."

Fear of retribution spreading

Thousands of opponents of the Assad regime have been tortured or killed in jails in Syria. In the course of the Syrian war, many have fled to Turkey and other neighboring countries and have sought to organize a political opposition that could force the Assad family from power.

But with the Syrian government, backed by Iran and Russia, now gaining the upper hand in the country's civil war, fear of retribution is spreading among this community.

That is why so many reacted to these killings by blaming the Syrian government, explained Rami Jarrah, a Syrian journalist who supports the opposition.

"It's too early a stage to determine whether the regime have begun a targeting campaign against Syrians dissidents abroad," he said Saturday. "But the fact that so many activists believe it was the regime is a sign of the genuine fear in this community now."

The Committee to Protect Journalists cited a local journalist, whom it did not name to protect the person's safety, who said that the Barakats had received death threats on social media and in emails from supporters of the Syrian government, but that they had not paid the messages much attention.

The CPJ has documented four other incidents of Syrian journalists being targeted in Turkey since 2015. In all of these cases, the militant group ISIS claimed responsibility.

The Barakat women had been close friends of Kayla Mueller, the American aid worker who was kidnapped by ISIS in 2013 and died while still being held hostage 18 months later.

Kayla's parents, Carl and Marsha Mueller, said in a statement to ABC News that "Orouba and Halla were like a mother and sister to Kayla."

"How many more?"

The shock of their deaths reached the United States, where the Barakat family has already suffered.

Extended family members Deah Barakat, wife Yusor Abu-Salha and her sister Razan Abu-Salha were shot dead in their home in Chapel Hill, N.C., in 2015. Their neighbor was charged, and authorities suggested during a preliminary investigation that the killings were not related to politics or religion.

"How many more beloved family members will I lose to hatred and violence?" Suzanne Barakat, a relative in North Carolina, wrote on Facebook. "We are not safe anywhere."

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