Sharon's comments in interviews with Israeli newspapers published on Friday were his most explicit threats yet against his arch foes.
Asked by Haaretz whether Arafat and Nasr Allah are targets for assassination, Sharon said: "I wouldn't suggest that either of them feel immune ... Anyone who kills a Jew or harms an Israeli citizen, or sends people to kill Jews, is a marked man. Period."
Sharon told Maariv Arafat "has no insurance policy."
The threat came 10 days after Israel's assassination of Hamas founder and spiritual leader Shaikh Ahmad Yasin by a helicopter strike in the occupied Gaza Strip.
Sharon has kept Arafat confined to his West Bank headquarters in the city of Ram Allah for more than two years.
Last September, Israel's cabinet declared Arafat was responsible for the Intifada or uprising against Israel's occupation and should be "removed." Several cabinet ministers have called frequently for his expulsion or killing.
Hizb Allah Secretary General Nasr Allah vowed earlier this week that his group would help Hamas retaliate Yasin's murder.
The US said it was opposed to any assassination attempt against Arafat, but stopped short of condemning Sharon.
"Our position on such questions - the exile or assassination of Yasser Arafat - is very well known. We are opposed and we have made that very clear to the government of Israel," Deputy Secretary of State Richard Armitage said on Friday.
Sharon also has warned that once Israel completes the controversial separation barrier it is building, cutting off parts of the occupied West Bank, more Palestinians would be expelled from Israel.
Jewish settlers do not want to
evacuate their illegal outposts
The Israeli premier claimed there are tens of thousands of "illegal" Palestinians in Arab-Israeli towns and villages.
At the height of international condemnation for Sharon's barrier-which cuts off some of the most fertile parts of the West Bank and separates tens of thousands of Palestinians from their homes-Sharon proposed his so-called "disengagement plan" from the occupied Gaza Strip.
This included unilaterally withdrawing from the occupied Gaza Strip and four small Jewish settlements in the West Bank.
Palestinians fear such a move will demarcate the borders of a future Palestinian state and cement Israel's hold on large Jewish settlement blocs.
Under international law, all Jewish settlements are illegal, a stance not recognised by Israel.
Sharon told the Maariv daily he hoped that by the spring of 2005, "we will be in the midst of disengagement, because disengagement is good for Israel."
Sharon has said he will leave the final decision on a withdrawal to his divided Likud Party. After his return from a 14 April meeting with US President George Bush, Sharon is to hold a binding referendum among 200,000 Likud members.
Recent polls suggested that while he has an advantage, the gap is too small to assure approval of the Gaza plan.
Palestinians took to the streets
to protest at Shaikh Yasin's killing
Sharon's interviews with the Maariv, Yediot Ahronot and Haaretz dailies, given before next week's Passover holiday, were seen as the opening of his campaign for the withdrawal plan.
The Prime Minister also told Yediot after the withdrawal Israel would consider cutting off water and electricity supplies to the Gaza Strip if resistance attacks continued.
On Thursday, American diplomats told skeptical Palestinian officials Israel's plan to pull out of Gaza would revive the US-backed "road map" aimed at ending the Palestinian-Israeli conflict.
The US envoys delivered the message in a meeting with Palestinian Prime Minister Ahmad Quraya. The team then had two hours of talks with Sharon, but no details were disclosed.
After Thursday's meeting, Quraya said he would welcome an Israeli pullback from Gaza, but only if it was part of the "road map".
Quraya said he sought assurances the Gaza plan would not prejudice future talks on a permanent settlement, including the status of the West Bank and occupied East Jerusalem and the right of return for millions of Palestinian refugees.
"Unilateralism is not the solution," Quraya said. "The only thing that will help and bring forth Palestinian commitments is to negotiate with the Palestinians."
In related developments, Israeli soldiers shot dead a Palestinian civilian during an invasion of the Gaza Strip overnight, according to medical sources.
Israeli military sources said the raid was ongoing.