"Ground and intelligence sources have confirmed that the Tigers are preparing to launch a major offensive south of Maavilaru, Kadjuwatte and Mankerni areas," the defence ministry said in a statement.
The military said the Liberation Tigers of Tamil Eelam (LTTE) had launched artillery salvos aimed at trapping civilians and had prevented food supplies from reaching several rebel-held villages.
"Continuous Tiger artillery shelling and mortar fire from Kadiraweli and Vakarai towards the Kadjuwatta and Manrkerni army camps have prevented food supplies reaching Vakarai," the ministry said.
The LTTE denied the charge and said it was the security forces who started shelling rebel-held areas and carried out an air attack on Monday afternoon.
"The military is shelling civilian villages and there were a couple of air raids this afternoon," Tiger military spokesman Rasiah Ilanthiriyan said by telephone when contacted in the rebel-held town of Kilinochchi.
He said the troops had also fired mortar