Mortars fell near a temple, church and a railway station in the Morakotanchenai village and wounded at least five civilians, the ministry said.
"Security forces facilitated members of the Sri Lanka Monitoring Mission to inspect the area and (visit) civilians injured in the attack," the ministry said. "Security forces retaliated and no damages were reported to troops."
Meanwhile, police said they found the bodies of three people shot dead in the district of Trincomalee. The motive was not immediately clear though defence officials suspect Tamil Tiger rebels were behind the killings.
The violence came as the military said the Liberation Tigers of Tamil Eelam (LTTE) are prepared to launch a major offensive against security forces in the island's eastern regions.
Tiger military spokesman Rasiah Ilanthiriyan on Monday denied the military claim and said they fired mortars in self defence.
Sri Lanka's key foreign aid donors -- the United States, European Union, Japan and Norway -- have asked both the government and the Tigers to refrain from military action even as peace talks between the combatants collapsed in Geneva last month.
Despite a truce in place since February 2002, nearly 3,300 people have died in fighting in the past year. Still, neither side has renounced the truce and both say they have only acted in self defence.
More than 60,000 people have been killed in Sri Lanka's drawn-out Tamil separatist conflict since 1972.

Copyright AFP (Agence France-Presse), 2006