SRINAGAR/NEW DELHI (Reuters) - India has shut at least four airports in the northern part of the country, a government official told Reuters, after Pakistani warplanes crossed a disputed border into the Indian side of Kashmir on Wednesday.

The escalation by Islamabad followed an Indian airstrike that targeted a militant camp inside Pakistan a day earlier.

India has shut airports at Pathankot, Leh, Srinagar and Jammu, the official said. Airports in Chandigarh and Amritsar have also been closed, an industry source told Reuters.

The main airport in Srinagar, the summer capital of Jammu and Kashmir state, had been shut down for three hours, police in the city said.