In a major diplomatic win for India, the United Nations on Wednesday added the leader of an outlawed Pakistani militant group to its sanctions blacklist after the group claimed responsibility for a February suicide attack in disputed Kashmir that killed 40 Indian soldiers.

Sanctions against Masood Azhar were confirmed by Pakistan’s Foreign Ministry spokesman Mohammad Faisal at a news conference in Islamabad. Mr. Azhar’s inclusion on the Security Council’s Islamic State and Al Qaeda blacklist comes with a travel ban and a freeze on his assets.

Wednesday’s development comes less than three months after Mr. Azhar’s group, Jaish-i-Mohammad, claimed responsibility for the Feb. 14 attack in Kashmir, which is split between the two countries and is claimed by both in its entirety. The clashes have brought the two nuclear rivals to the brink of war at times.