DAMASCUS, Syria — A masked gunman assassinated a well-known, elderly Dutch priest on Monday, shooting him in the head in the garden of a monastery where he lived in the central Syrian city of Homs on Monday, a fellow priest, an activist group and Syria's state-run media said.

Father Francis Van Der Lugt — a Jesuit, the same order as Pope Francis — had lived in Syria for decades and had refused to be evacuated with other civilians from the battleground city of Homs.

The motives for the attack were not known, and no one immediately claimed responsibility for the killing, which took place in Bustan al-Diwan, rebel-held neighborhood of Homs that has been blockaded for over a year by forces loyal to Syrian President Bashar Assad.

But the fact that Van Der Lugt was gunned down in a rebel-held area will likely underscore fears of many in Syrian Christian and Muslim minorities for the fate of their communities should Assad's government be overthrown by the rebels. Over the past year, hard-line rebel groups, including the al-Qaida-linked Nusra Front have become more influential and dominant among the opposition fighters in the city.

Vatican spokesman the Rev. Federico Lombardi said the 75-year-old Van Der Lugt, was "a man of peace, who with great courage, had wanted to remain faithful, in an extremely risky and difficult situation, to the Syrian people to whom he had dedicated, for a long time, his life and spiritual service."

It appeared that Van Der Lugt was directly targeted. A single gunman walked into the monastery, entered the garden and shot him in the head, said Rev. Ziad Hillal, a priest, who was in the convent when the attacked occurred.

"I am truly shocked. A man of peace has been murdered," Hillal said in a phone interview from Homs with the Vatican Radio.

Van der Lugt's death was first reported by Homs-based priest Assad Nayyef, the British-based Syrian Observatory for Human Rights and the state-run news agency, SANA.

An activist based in a blockaded rebel-area said rebel fighters were shocked by the priest's death.

"The man was living with us, eating with us, sleeping with us. He didn't leave, even when the blockade was eased," said Beibars Tilawi said via Skype. Regardless of the rebels' views toward Christians, the priest was well-liked for his efforts to get the blockade lifted and alleviate widespread suffering and hunger among civilians, Tilawi said.

In Belgium, the secretary of the Dutch Jesuit order Father Jan Stuyt said the slain priest had been living in Syria since the mid-1960s and was on good terms with the country's Muslim majority.

"He is like a martyr for the interreligious dialogue," Father Jan Stuyt said in a telephone interview with AP in Brussels.

Van Der Lugt repeatedly refused to leave Bustan al-Diwan, despite the violence and a series of U.N. evacuations this year that helped hundreds leave blockaded Homs areas.

A friend of the slain priest, who spoke on condition of anonymity because he feared for his safety, said Van Der Lugt refused to leave until all Christians were evacuated. The priest lived with 24 other Christians in the monastery.

It's not immediately clear how many Christians remain trapped in rebel-held parts of Homs. In February, there were about 200 Christian families, according to Syrian Red Crescent figures at the time.

The elderly priest also sought to raise widespread attention to the suffering of civilians in blockaded Homs.

"Hunger defeated us! We can see its signs drawn over the faces," Van Der Lugt wrote on Jan. 25 on a Syrian Christian Facebook group page.

"People are wandering the streets screaming; We are starving, we need food! They stop by the inhabited houses trying to find some food. Hunger breaks the rules and eliminates all moral principles," the priest wrote in a statement published in English and French. "We are living a scary reality. Human beings turn into wild animals living in the wild."

The friend said Van Der Lugt also fretted about the future of Christian properties inside rebel-held parts of Homs, which are frequently shelled and battered by Syrian government forces.

Albert Abdul-Massih, who worked along Van Der Lugt, said the slain priest held a doctorate in psychiatry and lived an austere life.

"He was a Christian clergyman but he wasn't conservative," Abdul-Massih said. "We learned humanity from him, and he used to love Muslims as much as he loves Christians ... He was treating people for free and he was a fluent Arabic speaker."

"He called me two days ago and told me that he is hopeful that the siege will end soon," Abdul-Massih added. "His death was a big loss."

The state-run news agency SANA blamed "terrorists" for the priest's death but offered no details. The government uses the term for anti-Assad armed rebels.

Syria's uprising, which began with largely peaceful protests against Assad's rule in March 2011, has evolved into a war with sectarian overtones.

Islamic extremists, including foreign fighters and Syrian rebels who have taken up hard-line al-Qaida-style ideologies, have played an increasingly prominent role among the rebel fighters, causing concern among Syria's many minority communities.

Another Jesuit priest, Father Paolo Dall'Oglio of Italy went missing in July after traveling to meet Islamic militants in the eastern city of Raqqa. The city fell into rebel hands in March 2013 and was subsequently taken over by radicals including the al-Qaida breakaway group the Islamic State in Iraq and the Levant.

Associated Press writers Diaa Hadid and Barbara Surk in Beirut, Frances D'Emilio in Rome, Mike Corder in The Hague and APTN producer Sandra Hodzic in Brussels contributed to this report.