US diplomats refused to comment, and US Ambassador John Bolton was in Washington preparing for a new confirmation hearing before the Senate; however, several diplomats said
Earlier Wednesday, UN officials said that the UN observers in Lebanon had in six hours to ask it to stop shelling near their position.
Jane Lute, assistant secretary-general for peacekeeping, told the UN Security Council in New York that the UN observation post near Khiam
UN officials said Hezbollah guerillas had been operating in the area of the post near the eastern end of the border with Israel, a routine tactic to prevent Israel from attacking them.
"We did repeatedly in recent days say (to Israel) that this was an exposed position, that Hezbollah militants were 500 meters (yards) away shielding themselves near UN workers and civilians," UN humanitarian chief Jan Egeland said. "That's why it is so inexplicable that what happened happened."
IDF officials had told the United Nations that the bombing around the base was part of an "an aerial preparation for a ground operation," said the senior official, who spoke on condition of anonymity.
Officials in the outpost called the IDF 10 times during those six hours, and each time an army official promised to have the bombing stopped, according to a preliminary UN report on the incident.
Once it became clear those pleas were being ignored, the force's commander sought the involvement of top officials in New York, a senior UN official in New York said.
UN Deputy Secretary-General Mark Malloch Brown and Lute herself then made several calls to Israel's UN mission "reiterating these protests and calling for an abatement of the shelling," Lute said.
Prime Minister Ehud Olmert expressed "deep regret" for the deaths and dismay over UN Secretary-General Kofi Annan's accusation that the attack was "apparently deliberate."
Olmert told Annan in a phone call Wednesday that the attack was inadvertent and he promised a "thorough investigation," his office said in a statement.
"It's inconceivable for the UN to define an error as an apparently deliberate action," Olmert said.
China called for an Israeli apology and asked the UN Security Council to condemn the bombing - which killed one of its citizens - and demand the IDF stop attacking UN positions and personnel.
"For China and for others, we condemn this because I think any attack on the United Nations positions and the United Nations personnel is inexcusable and unacceptable," China's UN Ambassador Wang Guangya said.
Austria and Finland, both of which also lost citizens in the attack, condemned the bombing, with Finnish Foreign Minister Erkki Tuomioja calling it "truly tragic." The fourth victim was Canadian.
Tuomioja said. "The longer this continues, the more likely it is that there will be more similar victims."
White House spokesman Tony Snow described the strike as a "horrible thing," but said Israel was behaving responsibly in its aftermath.
"They'll be completely transparent in the way they conduct the investigation," Snow said. "And I think that's the appropriate way to proceed."