Supporters of a hardline Bangladeshi preacher have heeded his call to counter fan frenzy around the World Cup by raising Islamic flags across the constitutionally secular country, putting police on alert, the force said Wednesday.

Football is extremely popular in Muslim-majority Bangladesh, with hundreds of thousands of fans supporting mainly Brazil and Argentina.

Mufti Harun Izhar, a Muslim religious leader, has urged supporters in a recent speech to take down the flags of Argentina and Brazil and raise white flags bearing the Kalima — profession of faith — wherever they could.

Such Islamic flags were raised in more than a dozen districts, leading police to say they would “act if these flags create a law and order situation”.

“We are on alert,” police spokesman Shahadat Hossain told AFP.