"I am devastated by the senseless killing of innocent people in Lahore on Sunday. My heart goes out to the victims and their families and friends," said Noble Laureate Malala Yousafzai.
"I condemn this attack in the strongest possible terms. We stand together with the families of the victims. Pakistan and the world must unite. Every life is precious and must be respected and protected," reported Geo TV.
The suspected suicide attacker blew himself up in the parking space of the Gulshan-e-Iqbal Park, a recreational park in the city.
A three days mourning has been declared in the Punjab province. Lahore is the capital of the province.
The Tehreek-i-Taliban Pakistan Jamaatul Ahrar has claimed responsibility for the blast. The United States has also strongly condemned the deadly suicide attack in Lahore.