Israeli air strikes on the Gaza Strip have killed at least 15 people in an escalation of the worst clashes with Palestinian militants so far this year.

The strikes began on Friday, when Israeli air raids killed the senior militant leader Zohair al-Qaisi, the secretary general of the Popular Resistance Committees (PRC). Israel claimed he was targeted because he was planning an attack.

Militants retaliated with a fierce rocket attack on Israel's southern border communities, which seriously wounded one civilian.

By Saturday, militants had fired 95 rockets at Israel – far more than the total number fired from the beginning of this year, an Israeli military spokesman said. He added that air defence systems intercepted around 25 rockets before they landed.

The Palestinian militants were killed in eight air strikes overnight and on Saturday morning, the Gaza health spokesman, Adham Abu Salmiya, said. He said civilians were also wounded by flying shrapnel.

Tens of thousands of Palestinian mourners marched through the streets in funeral processions following the deaths.

The most recent air strike targeted two Palestinian militants on a motorbike in the border town of Bani Suheila in the south-east of Gaza, Abu Salmiya said. Egypt said it was trying to broker a ceasefire.