LONDON -?The so-called Islamic State (IS) has claimed responsibility for Saturday's London attack, British media reported Sunday.

BBC reported on its website that the group's news outlet Amaq, on the messaging app Telegram, said "a security unit of Islamic State fighters carried out the London attacks yesterday".

Meanwhile, The Telegraph reported that an IS group propaganda outlet exhorted would-be jihadists to carry out vehicle and knife attacks on civilians just hours before three terrorists went on a rampage in central London.

According to the report, the message sent out on an encrypted messaging app, urging attackers to "gain benefit from Ramadan" and "kill the civilians of the Crusaders. Run over them by vehicles".

British police said 12 people have been arrested so far after the attack, which left seven people dead and 48 injured. Among the wounded, 21 people are in critical condition.