"It was the major pipeline. Militants dynamited it overnight only a few hours after the authorities repaired it," senior administration official Anwar Durrani told AFP in Baluchistan province, which borders Iran and Afghanistan.
The pipeline, which links the insurgency-hit province of Baluchistan to gas reserves at Sui, was blown up on Tuesday and had been down until repair work was completed late Wednesday, officials said.
Enayatullah Ismail, spokesman for the Sui Southern Gas company, confirmed the fresh attack but said it would take another two days to restore supplies to 200,000 consumers in the province.
"We are waiting for security clearance (before repair work can begin)," he told AFP.
The Baluch Republican Army militant group claimed responsibility for both attacks. Ethnic Baluch tribes are fighting for more political rights and a greater share of profits from the region's natural resources.