GENEVA: U.N. High Commissioner for Human Rights Navi Pillay denounced Israel's aerial attacks on the Gaza Strip as well as rockets fired by Hamas militants into southern Israel and called on both sides on Friday to step back from the brink.

"She's appalled that once again civilians are losing their lives... She urges both sides to pull back from an increasingly dangerous confrontation," her spokesman Rupert Colville told a news briefing in Geneva.

Two rockets fired from the Gaza Strip targeted Tel Aviv on Thursday in the first attack on Israel's commercial capital in 20 years, raising the stakes in a showdown between Israel and the Palestinians that is moving towards all-out war.

More than 20 people have been killed in the last few days, including seven children. Three Israeli civilians were killed in their home and several Palestinian children have also been killed, a baby among them, Colville said.

"The High Commissioner has repeatedly and unequivocally condemned the indiscriminate firing of rockets from the Gaza Strip into southern Israel and is deeply concerned by the recent major upsurge in the number of rocket attacks and that they are now being aimed at a major city such as Tel Aviv," he said.

"She is also extremely concerned by the sharp increase in aerial attacks by Israeli forces on the heavily populated Gaza Strip in the past two days," he said.

Israel authorities and the defacto authorities in Gaza have an obligation under international law to protect civilians, Colville said.