A Palestinian, wounded by an Israeli air strike, walks to the emergency room at al-Shifa hospital in Gaza City [AFP]

Israel has launched air strikes on Gaza, the third time in as many days, wounding four Palestinians including two children, security and medical officials from the territory have said.

Security officials and eyewitnesses said on Thursday that the Israeli aircraft hit three targets; two in the Gaza City and a third in Khan Younis, further south.

All of the sites were bases used by Hamas and other groups, the officials said.

The Israeli military confirmed that its aircraft had attacked Gaza but a spokeswoman could not immediately give details.

The strikes came at the end of a day in which at least five projectiles were fired into southern Israel from the Hamas-ruled Gaza Strip.

The rocket fire and air raids represented the first significant spike in violence in the area since April, when tensions rose after a missile fired from Gaza hit an Israeli school bus, killing a teenager.

Israel had responded with a series of strikes that killed at least 19 Palestinians in the deadliest violence since Israel's devastating 22-day assault on Gaza in 2008-2009.

Source: Agencies and Al Jazeera