Updated 4:10 pm: The Vatican on Monday voiced outrage over the killing of Dutch priest Frans van der Lugt in Syria's central city of Homs, saying he had been "a man of peace."

"According to his companions, he was taken away by two gunmen who beat him and then killed him with two shots to the head," Vatican spokesman Federico Lombardi said.

"This is the death of a man of peace, who showed great courage in remaining loyal to the Syrian people despite an extremely risky and difficult situation," he said.

Dutch Foreign Minister Frans Timmermans on Monday described the murder as "cowardly," saying his death should spur efforts to find peace.

"The man who brought nothing but good to Homs, who became a Syrian among Syrians and refused to abandon his people even when things became deadly dangerous, has been murdered in a cowardly manner," Timmermans said in a Facebook posting.

"Father Frans deserves our thanks and our respect. He must be able to count on our commitment to help end this misery," Timmermans added.

Van der Lugt spent nearly five decades in Syria, and told AFP in February that he considered the country to be his home.

He was renowned for insisting on staying on in besieged Homs despite daily shelling and dwindling supplies.

A Jesuit, Father Frans arrived in Syria in 1966 after spending two years in Lebanon studying Arabic.

"In this moment of great pain, we also express our great pride and gratitude at having had a brother who was so close to the suffering," Lombardi said.

The 75-year-old priest warned of the humanitarian suffering of the population in Homs in a video appeal earlier this year, saying people in Homs were living in misery and starvation.

"It's impossible that we suffer and the world does nothing," the Catholic priest said, speaking in Arabic.

Christians made up about 10 percent of Syria's population before the war erupted in 2011. The minority traditionally supported President Bashar al-Assad against the Islamist rebels, a stand for which they have been attacked.