The United States has vetoed a proposed U.N. Security Council resolution that urged international observers be sent to monitor the conflict between Israel and the Palestinians.

The vote was 12 in favor with Britain and Norway abstaining and the United States exercising its veto power.

The early Saturday morning session came after two days of closed talks among Council members.

The proposed resolution, sponsored by Tunisia, called for an end to the violence, including what it called "acts of terror, extra-judiciary executions and the excessive use of force." It emphasized that the Palestinian Authority is the "indispensable and legitimate party for peace." The resolution called on Israel and the Palestinians to return to peace negotiations and also encouraged the establishment of an international monitoring mechanism to "help create a better situation in the occupied Palestinian territories."

In explaining the veto, United States ambassador John Negroponte said the proposed resolution was one-sided. "Its purpose is to isolate politically one of the parties to the conflict, through an attempt to throw the weight of the Council behind the other party," he said. "One of the fundamental flaws of this resolution is that it never mentions the recent acts of terrorism against Israelis or those responsible for them."

Mr. Negroponte said it was "with regret" that the United States decided to use its veto power. It was the second time this year that the United States has vetoed a Security Council resolution on the Mideast conflict.

The head of the Palestinian Observer Mission, Nasser al-Kidwa expressed his regret that the Council has been "prevented from assuming its responsibility."