A farmer, 60, was killed outside his home by shrapnel on Saturday, Palestinian medical officials said.
Of the others, two farmers were injured when their tractor was hit, the officials said. A security officer manning a roadblock in the area, too, was wounded.
The army has frequently shelled the northern Gaza Strip in recent weeks in response to home-made Palestinian rocket fire.
Earlier on Saturday, the army dropped leaflets warning residents that it planned to fire artillery at rocket-launching grounds and urged civilians to avoid the areas.
"We warn you not to get close to the areas where rockets are launched in order to keep yourselves and your families safe," the leaflet said.
The army confirmed that artillery fire was going on at the time of the farmer's death. It was investigating the incident and declined further comment.
In early April, an 8-year-old girl was killed and eight relatives injured when tank shells hit their house.
Israel apologised, but said the artillery fire would continue as long as the rocket launchings continued.
On Friday, the Israeli military killed six Palestinians in two separate incidents in the Gaza Strip and West Bank.
Hamas MP in Sweden
Meanwhile, a Hamas cabinet minister thanked Sweden on Saturday for granting him a visa to attend a conference in the country, calling the controversial decision "a political message," news reports said.
"This good behavior sends a political message to our people - there is someone who loves justice," Swedish media quoted Atef Adwan as saying in a speech at a conference for refugee Palestinians in Malmo, southern Sweden.
Adwan was granted a visa to
attend a Palestinian conference
Sweden's decision to grant Adwan a visa has riled both Israel, which said it lent legitimacy to Hamas, and France, which recently rejected visa applications by other members of Hamas.
The group is listed as a terrorist organisation by the European Union and the United States.
The visa was issued by the Swedish consulate in Jerusalem this week, and allows Adwan to enter any of the 15 EU countries bound by the Schengen accords that allow for open border crossings.
Israel's foreign ministry and embassy in Stockholm harshly criticised the decision as counter-productive to international efforts to force Hamas to recognise Israel, accept past peace agreements and renounce violence.
Goran Persson, the Swedish prime minister, rejected the criticism, saying all 15 Schengen members had been notified of the visa application and that none had objected to it.
No Swedish government official will meet with Adwan during the visit.