Nuclear-armed neighbours India and Pakistan agreed to a ceasefire on Saturday after U.S. pressure and diplomacy, announcing a sudden stop to a conflict that had seemed to be spiralling alarmingly, Reuters reported.

But within hours, violations were reported from the main cities of Indian Kashmir, the territory that had borne the brunt of four days of fighting.

Blasts were heard in Srinagar and Jammu and projectiles and flashes were seen in the night sky over Jammu, similar to the events of the previous evening, according to authorities, residents and Reuters witnessed.

Military spokespeople in both countries did not immediately respond to requests for comment.

The fighting had been the worst between the old South Asian enemies in nearly three decades and threatened to erupt into a full-scale war in one of the world's most volatile and densely populated regions, according to Reuters.

There were briefly fears that nuclear arsenals might come into play as Pakistan's military said a top body overseeing its nuclear weapons would meet.