While the state-run Syrian Arab News Agency said a "terrorist group" was behind the attack, activists in Homs said the government was responsible, CNN reported.
The London-based Syrian Observatory for Human Rights, an opposition group, said government forces killed three civilians Tuesday in Homs.
"The regime did that intentionally," one activist said of the pipeline blast. "They don't care about Homs -- what difference does it make to them to have no power? We don't have any of the necessities: medication, heating fuel, food. And garbage is everywhere."
Two other activists told CNN the government blew up the pipeline to distract Arab League observers in Syria to monitor the government's commitment to end the violent crackdown against protesters. While Syrian tanks withdrew from residential areas in various cities, snipers still pose a threat and killings still occur, the head of the Arab League said Monday.
"There is still gunfire, there are still snipers, and we hope that all that will disappear," Secretary-General Nabil al-Arabi said from Cairo. "There is gunfire from various directions, which makes it hard to tell who is shooting. There is no doubt that killing is ongoing, but I can't pinpoint the numbers."
The observers arrived in Syria last week after the United Nations estimated at least 5,000 people had been killed since March in an uprising against President Bashar Assad's government, which has maintained it was cracking down on armed terrorists.
The Arab League leader said the organization was seeking a cease-fire and the names of detainees in Syrian prisons. Nearly 3,500 prisoners have been freed, al-Arabi said.
The Arab League has more than 70 monitors in six cities, he said, and the number of observers soon will top 100.
Arabi's comments differed sharply from observations attributed to the mission's leader, Lt. Gen. Mohammed al-Dabi, a former head of military intelligence in Sudan.
Dabi, a confidante of Sudanese President Omar al-Bashir -- wanted on war crimes charges by the International Criminal Court -- is accused of presiding over the creation of the Janjaweed government-backed militia that carried out a scorched-earth campaign in the Darfur conflict beginning in 2003.
In Syria, Dabi was reported to have said he saw "nothing frightening" during a gunfire-interrupted observer visit a week ago in Homs where more than 1,000 people were reported killed in some of the worst violence in the nine-month conflict.