Earlier, the officials reported that gun battles were taking place outside Spinkai Raghzai as well as Kalkala and Sharwangai.
On two flanks
Intelligence officials said the ground troops were advancing on two flanks and a northern front of a central part of South Waziristan controlled by the Mehsuds.
The areas being surrounded include the Taliban bases of Ladha and Makeen, the officials said.
The army says about 28,000 soldiers are battling an estimated 10,000 Taliban fighters, including about 1,000 Uzbeks and some Arab al-Qaeda members.
Speaking to Al Jazeera on Sunday, Hamid Nawaz, a former Pakistani general and military-affairs analyst, said he believed the army could complete its operations before the December snowfall.
"This is not going to be a set-piece battle ... the theatre of operations is only about 6,000sq km and there will only be pockets of resistance.
"And efforts have been made to co-ordinate attacks with Nato troops as well as the Afghan army on the other side of the border to prevent anyone escaping."
The Pakistani offensive comes after a series of bomb attacks across the country over the past two weeks that have killed more than 170 people.
In the latest attack, at least 11 people died in two explosions near a police office in the northwestern city of Peshawar on Friday.
People are reported to be fleeing from the Shakoi and Zangra areas, with many moving through North Waziristan where a makeshift camp has been set up at Mir Ali.
Wolfgang Herbinger, the country director for the World Food Programme, based in Islamabad, the Pakistani capital, said his organisation had readied itself for the exodus from the fighting.
"We have food stocks in nearby areas," he told Al Jazeera.
"As a United Nations organisation, we have been preparing for quite some time. We have had to anticipate in different parts of the country, including South Waziristan, that people will be on the move."
For weeks the army has been using air and artillery attacks on Taliban strongholds in South Waziristan and a curfew was put in place on Saturday.
Wajid Shamsul Hasan, Pakistan's high commissioner to the UK, said the offensive is difficult because the attacks are sporadic and spread out.
"It's difficult to fight them everywhere," he told Al Jazeera.
"That's why we were carrying out a softening operation through air raids and bombings. That's what we have been doing for the last four or five weeks.
"Now we think we are in a position to strike militarily on the ground in the spots we have been firing and mark them [Taliban] for attack. So I think we will be able to achieve our objective."
Imran Khan, Al Jazeera's correspondent in Islamabad, said: "South Waziristan is where Hakimullah Mehsud, the leader of the Pakistani Taliban, is based.
"And the police say that the carnage we have seen over the last 12 days is being planned from South Waziristan.
"So this is a crucial operation to decapitate the head of the senior Pakistani Taliban leadership ... But there is always the problem that if you squeeze the Taliban in one area, they pop up in another."
The US hopes that a Pakistani army operation in South Waziristan will help break much of the opposition network that threatens both Pakistan and American troops across the border in Afghanistan.