RAMALLAH, West Bank, Nov 16 (Jihan Abdalla/Reuters) - Palestinian President Mahmoud Abbas accused Israel on Friday of launching an assault on the Gaza Strip to undermine his efforts to secure a diplomatic upgrade at the United Nations.

Israel began its air offensive on Wednesday with the declared aim of stemming surges of rocket strikes by Islamist militants that have disrupted life in southern Israeli towns.

Abbas, whose forces were chased out of Gaza by Hamas in 2007, accused Israel of instigating a blood bath, telling reporters he thought the escalating military campaign was aimed at sinking his own diplomatic manoeuvrings.

Officials in Gaza say 28 Palestinians, including 16 civilians, had been killed since the start of the Israeli offensive. Three Israeli civilians were killed by a rocket on Thursday.

Everything that is happening is in order to block our endeavors to reach the United Nations, Abbas told journalists.

Islamist militants have fired hundreds of rockets into Israel over the past three days and there was a rare show of support for Hamas on Friday in Ramallah -- the de-facto Palestinian capital in the occupied West Bank.

Abbas, recognized by the West as the legitimate leader of the Palestinians in the Gaza Strip, has asked Arab League chief Nabil Elaraby to visit the enclave on Saturday and Sunday.

Undoubtedly we consider that this aggression is against us, the Palestinian people, he said.

PUSHING AHEAD

Despite the violence, he said he would push ahead with plans for a vote at the U.N. General Assembly before the end of the month to give the Palestinians the rank of an observer state within the world body rather than the present observer entity.

The upgrade would enhance Palestinians' legal rights at a time when peace negotiations with Israel have hit a wall over Israel's refusal to halt settlement building in territory where the Palestinians want their state.

We are going to the United Nations to vote on the resolution of our becoming an observer state on the 29th of this month. Nothing will deter us, Abbas said.

Both Israel and the United States have condemned the planned vote, which Abbas looks set to win, saying it violated the 1993 Oslo accords, which were intended to pave the way to a final status agreement within five years.

But on the streets of Ramallah on Friday thoughts were firmly focused on Gaza rather than far-away New York.

Hundreds of Hamas supporters marched on Ramallah's main square, waving green Hamas flags and chanting Hamas, onwards, onwards. Bearded young men carried posters of Ahmad Al-Jaabari, the Hamas military leader Israel assassinated on Wednesday.

What is happening in Gaza is a grave injustice, Ahmad Salem, 24, said. But I know that God is with us and he will liberate Gaza sooner or later.

Marking the sombre mood, local radio stations switched Arabic pop music for nationalistic songs, and daily cooking shows were traded for programs dedicated to Gaza's latest news.

We are here to say that this war is not against Hamas, but against the Palestinian people at large, Palestinian lawmaker Mustafa Barghouti told Reuters.

(Editing by Crispian Balmer)