William Hague has called for action to secure the release of three abducted hitch-hikers as Israel arrested dozens of Palestinians during the hunt for the youths.
The Foreign Secretary condemned the kidnapping in the West Bank, which Israeli PM Benjamin Netanyahu blamed on Hamas, saying he held the Palestinian Authority responsible for the disappearance.
Palestinians reject his claim and insist the trio went missing on Thursday in an area under Israeli control.
"I strongly condemn the abduction of three Israeli youths in the West Bank," Mr Hague said.
"My thoughts are with their families and I hope for their safe return home soon. I appeal to those who are able to bring about their release to take urgent action to do so."
Mr Hague said he was "deeply concerned by the escalation in violence on the ground" - including the "tragic" death of a child in an Israeli airstrike retaliation to rockets fired into Israel from Gaza.
"For the sake of both Israelis and Palestinians, I hope further escalation can be avoided.
"I call on all parties to respect in full the November 2012 ceasefire."