There has been sporadic violence despite the ceasefire
Mr Sharon accused the Palestinian Authority of failing to "stand by its commitments" to honour a ceasefire, after hearing of the killing.
The BBC's James Reynolds in Jerusalem says there is intense international pressure - led by the United States - on both the Israelis and the Palestinians to observe the ceasefire.
Our correspondent says the Bush administration wants to contain the conflict which will make it much easier to persuade moderate Arab states to sign up to its coalition against terror.
The latest violence throws into doubt hopes of a meeting between Israel's Foreign Minister, Shimon Peres, and Palestinian leader Yasser Arafat, to shore up the truce.
Group claims responsibility
Israeli police say 26-year-old Samrit Amrani was shot dead when gunmen fired on her car near the Jewish settlement of Tekoa.
Her husband, Shai, 32, was seriously injured in the attack.
A militant Palestinian group affiliated to Yasser Arafat's Fatah faction, Al-Aqsa Brigades, said it carried out the attack.
Speaking to reporters, Mr Sharon said: "I am very sorry the Palestinian Authority did not stand by its commitments and we will decide today how to act."
Mr Sharon has called for 48 hours of total quiet before he will allow Mr Peres to meet the Palestinian leader.
"Attacks prevented"
The Palestinians say they are making serious efforts to ensure the ceasefire remains intact.
Palestinian police are said to be patrolling trouble spots, including the Rafah refugee camp in the Gaza Strip, and the divided town of Hebron on the West Bank, to prevent any outbreaks of violence.
Speaking on Israeli military radio before the attack, Israeli Foreign Minister Shimon Peres said Mr Arafat had "prevented attacks in the past few hours and we have appreciated his intervention in this prevention".
But despite the ceasefire, violence has continued.
Two Jewish settlers were wounded, one of them seriously, in a bomb blast on Wednesday night near the Jewish settlement of Oranit on the border between Israel and the West Bank.
The Tanzim militia, affiliated with Yasser Arafat's Fatah faction, said they were responsible.
Earlier, Palestinian sources said a Palestinian man was killed, and five others were injured in an exchange of fire with Israeli forces in the divided West Bank city of Hebron.