At least 17 people, including women and children, were killed by Abu Sayyaf gunmen in southern Philippines on Monday.

The militants attacked two vans carrying civilians who were travelling to visit relatives and celebrate the end of the Muslim fasting month of Ramadan, military officials said, according to an Associated Press report. The attack was carried out near a coastal village in Talipao, on the island of Mindanao, by about 50 Abu Sayyaf militants armed with assault rifles, Marine Brig. Gen. Martin Pinto and other military officials reportedly said.

Fifteen people were killed when the militants opened fire on the vans, while two died at a hospital. Eleven other villagers were injured in the attack. The cause of the attack was not yet known but a family feud involving some of the militants could be the reason, Pinto reportedly said.

Among those killed were four members of a Talipao civilian security force called Barangay Police Action Team, AP reported, adding that, in recent months, the civilian security force had helped the military fight the militants, who are active in the country's Muslim-dominated south.

Abu Sayyaf, which was formed in the southern Philippines during the early 1990s, consists of about 300 armed fighters divided into many factions. The group has been pushed back to the jungles and has largely been crippled by a U.S.-backed Philippine military offensive, forcing it to survive mainly on ransoms from kidnappings in the region, the report said. The group currently holds about 10 hostages, which include two German tourists kidnapped in April and two other European tourists who were kidnapped two years ago, AP reported.

In a country where the majority population is Roman Catholic, Abu Sayyaf is one of four smaller Islamist insurgent groups that did not accept a peace deal signed by the Philippine government in March with the Moro Islamic Liberation Front -- the country's largest rebel group with 11,000 members. The Islamist groups demand the creation of a large autonomous region for the country’s Muslim minority in the south.