An explosion in central Istanbul on March 19 killed at least four and injured 20 others, three of whom are reported to be in a critical condition, underlining the worsening security conditions in Turkey.

CNN Turk reported that this was a suicide bomb attack and the bomber was among dead.

The authorities immediately imposed a ban on media coverage of the blast in Istiklal, close to Taksim square that was scene of demonstrations two years ago and is a busy pedestrian way. 

The explosion occurred on Istiklal Street at around 11:00am Istanbul time, one of the city’s major tourist attractions with hundreds shops and restaurants, packed with people during the day.

Police sealed off the street after the explosion, ambulances were dispatched to the scene of the blast.

The Istanbul explosion comes shortly after a suicide car bomb attack killed at least 34 people and wounded 125 more in in the heart of Ankara on March 13, less than a month after a similar attack on a bus carrying military and civilian personnel killed 29 in the same area.

The militant Kurdish Freedom Hawks (TAK), an offshoot of the outlawed Kurdistan Workers’ Party (PKK), claimed responsibility for both attacks in Ankara.

Germany closed its diplomatic missions in Istanbul and Ankara as well as German schools until the weekend due to the increasingly poor security situation in Turkey. 

German magazine Der Spiegel reported that the U.S. CIA, the Turkish secret service and Kurdish security sources told German's foreign intelligence service that a suicide attack linked to Islamic State was planned on German diplomatic missions or the schools until Sunday.

Islamic State militants have carried out several deadly attacks in Turkey in the last year. A suicide bomb attack in the town of Suruc, near the Syrian border, killed at least 30 in July 2015. Islamic State militants targeted a peace rally in Ankara in October 2015, killing more than 100 people.

At least 10 German tourists were killed in a suicide bomb attack, also blamed on Islamic State, in January this year in Istanbul’s Sultanahmet district.