PORT AU PRINCE -- Haiti's already fragile government faces a serious new crisis after one of the island's increasingly brazen criminal gangs kidnapped a large US missionary group.

There has been little official reaction in Haiti, and local police did not immediately respond to an AFP request for comment, but civil groups called Sunday for the immediate release of the group of 15 to 17 missionaries, family members and staff abducted a day earlier while returning from an orphanage visit.

"We call for the liberation of the persons kidnapped, whether American citizens or of other nationalities," said Gedeon Jean, director of the Center for Analysis and Research in Human Rights, based in the capital Port-au-Prince. He said the current situation was "detrimental to human dignity."

The missionary group, including children and by some accounts one Canadian, was traveling in several vehicles when stopped by members of a criminal gang some 30 kilometers (20 miles) east of the capital, a Haitian security source told AFP.

- 'Pray for us!' -

One member of the group posted a desperate call for help in a WhatsApp group even as the attack unfolded, The Washington Post reported. "Please pray for us!!" the message read. "We are being held hostage, they kidnapped our driver. Pray pray pray. We don't know where they are taking us."

An audio message from Ohio-based Christian Aid Ministries said that "men, women and children" were being held, adding, "Pray that the gang members will come to repentance and faith in Jesus Christ," the Post reported.

The group did not immediately respond to a request for comment.

The abduction was the work of the so-called "400 Mawozo" gang, which for months has carried out kidnappings and robberies in the area between Port-au-Prince and the Dominican Republic border, said a Haitian security source, who spoke on grounds of anonymity.

The gang has hijacked several vehicles -- even entire busloads of victims -- on roads it controls, kidnapping both Haitians and foreigners and holding them for ransoms often many times a Haitian's yearly earnings.

Such armed gangs have been steadily extending their reach, taking advantage of spreading insecurity and a political crisis aggravated by the assassination in July of President Jovenel Moise.

"The police have proven incapable of confronting the gangs, which have become better organized and which control more and more territory" around the capital and in provincial cities, Gedeon Jean said.

His group has tallied an alarming increase in kidnappings in Haiti: more than 600 occurred in the first three months of 2021, up sharply from 231 in the corresponding period of 2020.

The US State Department offered no details on the situation.

A spokesperson said only: "The welfare and safety of US citizens abroad is one of the highest priorities of the Department of State.

"We are aware of these reports and have nothing additional to offer at this time."

Officials are typically close-mouthed about abductions, given the extraordinary sensitivity of such situations.

- Turmoil -

In April, the Mawozo group held 10 people, including two French Catholic clergy members, for 20 days before releasing them.

The gangs often demand huge ransoms. Rights groups say the vast majority of women kidnapped by criminal gangs are sexually assaulted.

Haiti has struggled for years with natural and man-made challenges that have fueled disorder and paralyzed economic growth.

Barely a month after Moise's assassination in the presidential residence, an August 14 earthquake killed more than 2,200 people in the southwest.

Gedeon Jean said the absence of a strong state has left a void that criminal gangs have moved to fill, extending their hold from some of the capital's poorest districts into surrounding areas.

Even before Saturday's kidnappings, business and professional groups in Port-au-Prince had called for an indefinite strike beginning Monday to protest the spreading climate of insecurity.