Two intelligence officials said the army's 14th Division was being redeployed to Kasur and Sialkot, close to the Indian border. They said some 20,000 troops were on the move. Earlier Friday, a security official said that all troop leave had been canceled.
The officials spoke on condition of anonymity because of the sensitivity of the situation.
Indian officials could not be immediately reached for comment.
An Associated Press reporter in Dera Ismail Khan, a district that borders the Afghan-frontier province of South Waziristan, said he saw around 40 trucks loaded with soldiers heading away from the Afghan border.
India is blaming Pakistan-based militants for last month's attacks on Mumbai. Islamabad has said it will cooperate in any probe, but says it has seen no evidence backing up India's claims.
Both countries have said they hope to avoid military conflict, but Pakistan has promised to respond aggressively if India uses force, an option the Indian government has not ruled out.
Pakistan has deployed more than 100,000 soldiers in Waziristan and other northwestern regions to fight Islamic militants blamed for surging violence against Western troops in Afghanistan.
A senior security official refused to comment directly on Friday's troop movements, but said, "Necessary defensive measures have been taken, they are in place and Pakistan's armed forces are prepared to tackle any eventuality."
He asked his name not be used, citing the sensitivity of the situation.
Pakistan and India have fought three wars since their independence from Britain in 1947.