According to an official communique released by the outfit, it plans more attacks.

Following the incident, threat level in the city has been raised to 'critical', London Mayor Sadiq Khan tweeted.

"The national threat level has been raised to 'critical' after the terrorist attack at Parsons Green," Khan's tweet read.

However, experts have said that the ISIS often seeks credit for attacks that have no links with it.

Reacting to the blast, British Prime Minister Theresa May said, "This was a device intended to cause significant harm."

An assessment by experts said that the device contained a timer and hence the bomb was made by a professional.

Meanwhile, a tweet by American President Donald Trump following the attack, sparked backlash from the British Prime Minister.

In his tweet, Trump had said, "Another attack in London by a loser terrorist. These are sick and demented people who were in the sights of Scotland Yard. Must be proactive!"

His tweet came at a time when neither the Met Police nor the London government had made anything public about the investigation and kept it as a suspected terrorist attack.

Reacting to Trump's tweet, May said that it's not good to speculate, without naming the US President.

It's not "helpful for anybody to speculate on . . . an ongoing investigation," she said.

In the recent past, Britain has witnessed a surge in terrorist activities.