An exterior view shows a national guard base after a recent suspected Islamist militant attack in Aktobe, Kazakhstan, June 7, 2016. REUTERS/Olzhas Auyezov

ASTANA (Reuters) - Gunmen who attacked a national guard base in Kazakhstan last week listened to a broadcast from Syria beforehand that urged them to wage holy war, the country’s interior minister said on Tuesday.

Five civilians and three servicemen died in the June 5 attack in the city of Aktobe, the deadliest in Kazakhstan since it became independent in 1991. Security forces killed 18 gunmen, some in a subsequent manhunt.

Kalmukhanbet Kasymov said the suspects had some time earlier listened to an audio address from “a so-called imam”, probably from Syria, who called for “jihad”, or a war against unbelievers.

The minister provided no further details and did not specify if he was referring to territory held by Islamic State.

No group has claimed responsibility for the attack, which Kazakh President Nursultan Nazarbayev blamed on Salafist militants, followers of an ultra-conservative form of Islam.

One of the men held responsible by Kazakh authorities had posted a video online sympathetic to Islamic State.

A message issued on May 21, purporting to come from a spokesman for the jihadist group, called on followers abroad to launch attacks during the Islamic holy month of Ramadan, which began in early June.

A Russian version of the message can be found on social network Vkontakte, used by several people who were on a list of Aktobe suspects that was leaked to Kazakh media.

Some 300 Kazakhs have left the country to join Islamic State in Syria and Iraq, half potential fighters and the rest family members, according to government estimates.