US President Barack Obama has condemned the "senseless slaughter" of four Israeli settlers, as a new round of Middle-East talks opens in Washington.Mr Obama spoke after meeting Israeli PM Benjamin Netanyahu, on the eve of the first direct talks between Israeli and Palestinian leaders in 20 months. He will meet Palestinian leader Mahmoud Abbas later on Wednesday. Mr Netanyahu said Tuesday's killings near Hebron were committed by people who "butcher everything they oppose". US, Israeli and Palestinian officials have said they will not allow the shootings of the four Israelis to derail the new momentum in the long-stalled Middle East peace process. Disagreement over Israeli settlement construction in the occupied West Bank has also threatened to cast a pall over the talks. The Israelis have said they will not renew a partial freeze on building homes for Jews there when it expires at the end of this month, but the Palestinians say that without a freeze they will walk away from the talks.