The Sri Lanka military has carried out a series of air attacks against suspected Tamil Tiger positions in the north-eastern district of Trincomalee.
A government minister said the attacks were intended to help engineers gain access to the Maavilaru canal.
Officials accuse the Tigers of blocking the canal and preventing the irrigation of thousands of acres of farmland. Reports say two people were injured.
Antonio Guterres, UN High Commissioner for Refugees, had just left the area.
Government minister Keheliya Rambukwella said the raids had been carried out to give cover to ground troops escorting engineers to the canal.
"We were sending irrigation engineers to open the sluice gates that had been closed by Tigers," Mr Rambukwella told the AFP news agency.
"But they could not move without the support of troops.
"We have taken several targets by air in support of the ground troops who escorted the engineers because they were afraid to go on their own."
There was no immediate response from the Tamil Tigers.
Local journalists told the BBC Tamil service two people had been injured in the attacks and two houses damaged.
The Sri Lankan air force has carried out a number of air attacks on suspected rebel positions in recent months as a 2002 ceasefire has teetered on the verge of collapse.
Mr Guterres wanted to assess for himself the security and housing needs of the growing number of internally displaced people in north-east Sri Lanka.
He is meeting government officials and Tamil Tiger rebels during his three-day trip.
More than 300,000 Sri Lankans have been displaced by three decades of fighting.
A further 500,000 were made homeless by the devastating tsunami of December 2004. Correspondents say many are still in temporary accommodation.
The situation has been further complicated by a surge in violence this year, causing 50,000 people to flee their homes.