Why is Pakistan building underground tunnels close to Indian borders for Nuclear Missiles

Pakistan is reportedly building underground tunnels to store a stock of 140 nuclear weapons. The underground tunnels are being dug reportedly in Mianwali, which is located 350-km from Amritsar and 750-km from New Delhi. According to a report on Wion, the area where the tunnel is built comprises three interconnected tunnels, each 10 metres in height and 10 metres in width. The retired Indian Army officer also stated in the report that the tunnels are further linked by wide roads, broad at the corners to facilitate the movement of transporter erector launchers from where missiles are filed. All the tunnels have separate entry and exit gates. Available intelligence suggests that each tunnel can store anything between 12 and 24 nuclear weapons. The colonel, who is a military intelligence veteran of the Indian Army and an expert in satellite imagery analysis said that India needs to monitor this site frequently. According to Bulletin of Atomic Scientists in its latest report said that Pakistan is expanding its nuclear arsenal and has developed an estimated stockpile of 130 to 140 warheads for delivery as well as converting some of its fighter jets, including F-16s to deliver nukes. Earlier, Pakistan's top diplomat had warned India against launching surgical strikes or targeting the country's nuclear installations, saying nobody should expect restraint from Islamabad if that happens.