Israeli air strikes hit seven targets in the Hamas-run Gaza Strip early Friday, killing two men and wounding two others, Palestinian medics said.
The casualties occurred near Gaza's border with Egypt when Israeli jets bombed two tunnels, which Palestinians use to smuggle goods into the besieged coastal strip, medics and Hamas security officials said.
The raids came after Palestinians fired more than 10 mortars and a rocket into Israel Thursday without causing casualties, according to the military.
Israeli aircraft also hit three targets near Gaza City and two near the southern town of Khan Younis, witnesses and Hamas officials said. All the strikes hit empty buildings or open spaces.
The army had no immediate comment.
On Thursday, Israeli planes dropped thousands of leaflets over the Gaza Strip warning residents to stay clear from the border after Palestinian militants fired mortar shells into Israel.
The letters, which were dropped over northern Gaza and Gaza City, warned residents not to get within a range of 300 metres (yards) from the heavily secured border with Israel.
"Anyone who gets closer than this will be in danger," the leaflet read in Arabic.
Palestinian militants earlier fired a salvo of more than five mortar shells that fell near the Israeli community of Kerem Shalom, causing no casualties or damage, an army spokesman said.
As a result, Israel closed down the Kerem Shalom crossing with the Gaza Strip "until further notice," the defence ministry said in a statement.
The strikes marked the latest violence along Gaza's border, which has been mostly quiet since a war Israel launched on the Islamist Hamas in Gaza on December 27, 2008 in response to rocket fire ended with mutual ceasefires on January 18.
The ceasefires have largely held, despite violations by both sides.