The group of seven were on a study visit to Nigeria. They were held by police in the northern city of Kano after leaving their hotel during the night, against local security restrictions.

The curfew was imposed after demonstrations that broke out against the government turned violent in early August, leaving several people dead.

The seven Poles were not formally arrested but were held at their hotel in the city, the onet.pl news site reported.

The Foreign Ministry in Warsaw said in a tweet that the group were currently in Kano, and posted a video of Polish Foreign Minister Radosław Sikorski speaking by phone to a representative of their families.

A Foreign Ministry spokesman said last week that “absurd” claims that the group had been waving Russian flags at the protest had disappeared, and that they had merely been in the wrong place at the wrong time.