Aljazeera's correspondent in Islamabad reported that an unknown group attacked the gas pipeline on the Khamri Bridge between Sui and Quetta in southwestern Pakistan.
The blast caused a partial disruption of gas supplies in the region.
The explosion coincided with a visit by a parliamentary delegation charged with investigating disturbances in the region.
In another attack on Tuesday night, an office of the ruling faction of the Pakistan Muslim League was destroyed by a blast in Turbat town, in the west of the province. No one was wounded in either blast.
"A four-foot (1.5-m) section of the pipeline was blown up," security force commander Khair Muhammad Jamali said in the provincial capital, Quetta.
The ruptured pipeline, which supplied gas from Shikarpur to many parts of the province, was sealed off after the attack.
Baluch tribesmen have been
waging an uprising for decades
Ethnic minority Baluch rebels have been waging a low-level uprising in the province for decades for greater economic and political autonomy, but they have recently stepped up attacks on targets such as natural gas pipelines, electricity pylons and railway lines.
Security has been tight since an attack on the country's largest gasfield in Sui on 11 January, in which 15 people were killed.
Last Thursday, eight soldiers were killed and 23 wounded in a battle with the fighters on the outskirts of Dera Bugti town. A tribal leader said 62 people were killed on his side.
Hundreds of fighters have surrounded a security post in the remote town since the battle, and a top commander said on Tuesday the confrontation could degenerate into a major crisis unless a political solution could be found.
The unrest in Baluchistan is the latest security headache for President Pervez Musharraf's government.
Troops have been confronting rebels on the rugged western border with Afghanistan for the past year and the authorities are also trying to end sectarian violence between fighters from the majority Sunni and minority Shia communities.
In the 1970s, the government launched a sweeping campaign against Baluch fighters, largely ending their agitation for several years.