The latest explosion on a bridge in the south-western city on Thursday injured four police personnel and nine passers-by, in an attack apparently targeting a judge.
SITE reported that the IS group claimed the attack on its Telegram channel, al-Bayan Radio and Twitter.
The attack came just days after a suicide bombing at a hospital on Monday also claimed by the IS group killed 73 people, most of them senior lawyers gathered to mourn a colleague gunned down earlier in the day.
Quetta is the capital of the mineral-rich province of Balochistan, which is plagued by roiling insurgencies, hit by regular militant attacks and run by political leaders accused of corruption.
Lawyers are among the only people shining a spotlight on the province’s many problems and have come under frequent attack.
Monday’s bombing was also claimed by the Jamaat-ul-Ahrar faction of the Pakistani Taliban and analysts have been unclear on whose claim was more credible.
Islamic State militants have been struggling to gain a foothold in Pakistan, facing competition from well-established extremist groups such as the Pakistani Taliban.
