Obama warns: Don't let peace talks 'slip away'

US President Barack Obama will meet face-to-face with the leaders of Israel and Palestine for the first direct peace talks over the volatile West Bank in almost two years.

Israeli Prime Minister Benjamin Netanyahu and Palestinian Prime Minister Mahmoud Abbas meet in Washington after a 20-month hiatus to try and solve unrest between the two states.

Obama, who has staked considerable political capital on the Washington talks, urged both sides to grasp the chance for peace after separate meetings at the White House on Wednesday.

"This moment of opportunity may not soon come again. They cannot afford to let it slip away," Obama said.

The Palestinians say they will drop out of the negotiations unless Israel extends a law stopping Jewish settlement construction in the occupied West Bank when it expires this month.

However, Netanyahu, who heads a coalition dominated by pro-settler parties, has resisted any formal extension of the partial construction freeze.

Four Israeli settlers were killed by the Islamist Palestinian group Hamas in a shooting attack in the West Bank on Tuesday and another two people were injured in a similar attack by suspected Palestinian gunmen on Wednesday.

The talks are also seen as a test of Obama's faltering drive to improve ties with the Muslim world as he pushes for a united front against Iran's nuclear ambitions.