Israel has launched air attacks against targets in the Gaza Strip, injuring eight Palestinians, medical sources have said.

Sami Zyara, a Palestinian journalist in the Gaza Strip, told Al Jazeera that at least two rockets launched on Friday targeted a police training centre run by Hamas.

The Israeli military had no immediate comment.

Earlier on Friday, Palestinian fighters launched a rocket into the city of Ashkelon on Israel's Mediterranean coast, causing some damage but no injuries. 

There are also reports that israeli rockets have hit smuggling tunnels on the border with Egypt, without causing casualties.  

"This attack came after rockets were fired at Ashkelon," Zyara said.

He said that injuries were less than they could have been, given the crowded area that was hit, because Palestinians expected that "Israel would retaliate" for the attack on Askkelon.

"None of the Palestinian groups declared responsibility for that attack," he said.

Binyamin Netanyahu, the Israeli prime minister, said that "Israel takes the firing on Ashkelon very seriously".