The force used by Israel in its attacks on Hamas militants in Gaza is "disproportionate", the department of international relations said.
Briefing media in Cape Town, International Relations and Cooperation Minister Maite Nkoana-Mashabane said the South African government was gravely concerned at the escalating violence between Israel and Gaza.
"We strongly condemn the disproportionate use of force by the Israeli government, which has resulted in a significant number of deaths and injuries ... particularly among Palestinian civilians, including children."
The government called on both sides to halt all cross-border attacks and agree to a ceasefire.
"Israeli air and naval forces must cease their air strikes and shelling into the Gaza enclave ... We also call upon Palestinian militants in Gaza to immediately suspend the firing of rockets into Israeli territory," said Nkoana-Mashabane.
Reports earlier on Tuesday were that Israel had put plans for a ground attack on Gaza "on hold" to give peace talks – brokered by Egypt – a chance.
According to the BBC, Israel has set a Thursday deadline for the talks to succeed.
Nkoana-Mashabane said Israel's decision to call up tens of thousands of military reservists to active service was an "ominous development", and implied a large-scale ground assault into Gaza was being contemplated seriously.
"The South African government accordingly appeals to the government of Israel to refrain from such a fatal step, which will not only result in the inevitable loss of a large number of both Palestinian and Israeli lives, but also further inflame sentiments in an already volatile region."
The week-long Israel-Gaza violence follows an Israeli air strike, on November 14, that killed the commander of Hamas's military wing, Ahmed Jabari.
Nkoana-Mashabane condemned the killing, saying it was "in violation of international laws".
Those who engaged in such activities needed to be called to account by the United Nations. The minister said she would meet the South African Jewish Board of Deputies on Wednesday, to "raise our concerns" about the conflict.
Asked if South Africa had any plans to withdraw its ambassador to Israel, she responded: "That is a decision we will take at the appropriate time." – Sapa