The ministry said the Liberation Tigers of Tamil Eelam (LTTE) had stepped up artillery and mortar attacks against security forces since the collapse of talks in Geneva last weekend.
Government forces hit back on Thursday with air strikes against the Tigers' northern stronghold of Kilinochchi.
Foreign truce monitors confirmed that bombs hit an area just outside the hospital, killing five people.
The hospital suffered minor damage.
"These sporadic artillery and mortars attacks have intensified, but were repulsed successfully by the security forces," the Sri Lankan defence ministry said.
It also said the LTTE had sent more of its fighters to the island's embattled east during the two-day talks in Geneva.
"The situation created by the Tiger terrorists (indicates) that they will launch their attack in the east prior to the birthday of their leader on the 26th," the ministry said.
Tiger supremo Velupillai Prabhakaran turns 52 on November 26.
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His birthday also coincides with the r