Pakistan is ready to help India investigate the deadliest blast in Kashmir in decades, but will retaliate if New Delhi attacks, Prime Minister Imran Khan said on February 19 as tensions between the two countries soared in the wake of the Pulwama attack.

“Pakistan won't just think to retaliate. Pakistan will retaliate,” said Mr. Khan in a nationally televised address.

Mr. Khan went on to demand New Delhi share proof of Islamabad's involvement in the suicide blast, which killed 40 CRPF jawans.

He spoke days after the attack was claimed by Pakistan-based militant group Jaish-e-Mohammed, unleashing a war of words between the two countries and spurring both to call their respective envoys for consultation.

India has accused Islamabad of harbouring the militants and vowed “the terrorist groups and their masters... have to pay a heavy price”.

Pakistan has denied involvement. Mr. Khan vowed on February 19 that if any militant group was using Pakistani soil to launch attacks, “its enmity is with us. This is against our interest”.

Minutes after the address, Mr. Khan’s official Instagram account posted a picture of the premier — scowling and cross-armed — along with a message that read: “Don't mess with my country”.

Earlier in the day, Foreign Minister Shah Mahmood Qureshi pleaded with U.N. Secretary General Antonio Guterres to intervene, saying India was threatening to “use force against Pakistan” and abandon a vital water treaty.

“It is imperative to take steps for de-escalation. The United Nations must step in to defuse tensions,” wrote Mr. Qureshi in a message shared with journalists.