Hamas declares ceasefire in Gaza

Hamas says it has brokered a deal for Gaza's militant groups to stop firing on Israel, after another day of violent exchanges.

Hamas, which governs Gaza, said the truce was designed to stop an escalation of Israeli "aggression".

The militant wing of Hamas earlier hit an Israeli bus with an anti-tank shell, injuring two people.

Israeli forces replied with air strikes and tank fire, killing four and wounding 30, Palestinian doctors say.

The bus attack was condemned by the US, which said it was particularly concerned by reports that the Gaza militants had used an advanced anti-tank weapon to target civilians.

The bus had been dropping off schoolchildren near the Nahal Oz kibbutz, and was carrying only one passenger when it was hit, Israeli medical sources said.

A 16-year-old boy suffered a serious head wound and was taken to hospital for surgery.

After the attack, witnesses said more rockets and mortars were fired from the Gaza Strip.

In response, an Israeli plane bombed a compound in northern Gaza belonging to Hamas. Targets in Gaza City and Rafah were also hit.

Israeli Prime Minister Benjamin Netanyahu said Israel would take any action necessary to deter attacks from Gaza.

"We hope this situation will be contained but we will not shy away from taking all the necessary action, offensive and defensive, to protect our country and to protect our citizens," said Mr Netanyahu during a visit to Prague.

Later, the Hamas Interior Ministry announced it had been in talks to broker a truce, saying: "We received a positive response from most of the factions."

The ministry did not announce which groups had refused the truce.

Officials said the ceasefire went into effect at 2300 local time (2000 GMT).

Riyad Mansour, the top Palestinian diplomat at the UN, said he hoped Israel would also respect the move.

Last month saw some of the worst violence since Israel launched a major offensive in Gaza in December 2008.

In one week in March, at least 10 Palestinians - including several civilians and children - were killed by Israeli attacks.

In the same period, militants in Gaza fired more than 80 rockets and mortar shells into southern Israel.

Israel says it holds Hamas responsible for all attacks coming out of Palestinian territory, even if it is other militant groups carrying them out.