RAMALLAH, Palestinian Territories (AFP) - Palestinian president Mahmud Abbas described as "despicable" on Tuesday a threat by the Islamic State in Iraq and Syria (ISIS) group to kill two Japanese hostages and pledged his full support to visiting Prime Minister Shinzo Abe.

"We once again emphasise our condemnation and total rejection of such despicable acts... which go against human morality," Abbas said at a joint news conference after talks with Abe in the West Bank city of Ramallah.

"We express our solidarity with you, and we stand by your side," he told Abe, who shared the podium with him.

For his part, Abe said he had promised about $100 million (S$130 million) to help reconstruction efforts in the war-ravaged Gaza Strip.

"We are preparing to give more support, worth around US$100 million, in humanitarian aid, reconstruction aid and financial aid to Palestinian civil authorities," he said.

More than 100,000 Gaza homes were destroyed or damaged during last year's 50-day war with Israel, and UN welfare officials say that 17,000 displaced people are still living in schools.

After meeting Abbas, Abe was to fly back to Japan several hours earlier than scheduled.