Switzerland is the home of the Geneva Conventions, which set out the rules of armed conflict. It is the Swiss government's responsibility to convene and host conferences when changes are needed.

"A number of actions by the Israeli Defence Force [Israeli army] in their offensive against the Gaza Strip have violated the principle of proportionality ... and are to be seen as forms of collective punishment, which is forbidden," the foreign ministry said in a statement.

It said there was "no doubt" that Israel had not taken the necessary precautions required of it under international law to protect the civilian population and infrastructure.

The destruction of a power station, supplying 43% of the Gaza Strip's electricity, the attack on the office of the Palestinian prime minister and the arbitrary arrests of large numbers of democratically elected legislators could not be justified, the Swiss ministry said.

The statement appealed to the captors of an Israeli soldier to treat him humanely. It also said that any measures Israel undertook to free him must be in line with international humanitarian law.

Switzerland's statement came as Israel warned Hamas, the Palestinian governing group, that the "sky will fall on them" after a deadline set by the fighters for Israel to free prisoners in exchange for the soldier expired.

Three Palestinian factions in the Gaza Strip, among them the armed wing of Hamas, had given Israel until 6am local time, saying it must respond by then if it valued the life of Corporal Gilad Shalit, 19, seized in a cross-border raid on June 25.