Issuing a security advisory, the Principal Secretary (Home) said: 

In the wake of intelligence inputs of specific ‘terror threats’ to the Amarnath pilgrimage, the J&K government has asked all the yatris to return as soon as possible. 

All tourists as well as devotees were issued a notice to cut short their stay, reports the Times of India.  

Kashmir Life
Keeping in view the latest intelligence inputs of terror threats, with specific targeting of the Amarnath Yatra, and givem the prevailing security situation in Jammu & Kashmir Valley, in the interest of safety and security of the tourists and Amarnath Yatris, it is advised that they may curtail their stay in the Valley immediately and take necessary measures to return as soon as possible. 
Times of India

Earlier today, the Indian army recovered a Pakistani-made mine and huge caches of arms from along the Amarnath Yatra route. 

Searches were launched based on different pieces of intelligence from multiple agencies to make sure the Yatris are secure. 

Financial Express

Fearing eruption of fresh violence from terrorists in the valley, the Indian army also sent 25,000 additional troops to Jammu & Kashmir to take control of the situation.