BEIRUT, Lebanon -- The U.N. observers killed when an Israeli bomb hit their bunker in Lebanon Tuesday called an Israeli military liaison about 10 times in the six hours before they died to warn that aerial attacks were getting close to their position, a U.N. officer said.

After each call, the Israeli officer promised to have the bombing stopped, an officer at the U.N. Interim Force in Lebanon (UNIFIL) base in Noqoura said.

Finally, an Israeli bomb exploded directly on the U.N. post near Khiyam, killing four U.N. observers from Austria, Finland, Canada and China, the U.N. officer said.

As of Wednesday morning, three of the four bodies had been recovered from the rubble, an officer at the UNIFIL base in Noqoura said.

Israeli Foreign Ministry spokesman Mark Regev said the incident would be "thoroughly investigated" and that the Israeli military had taken measures since the start of its bombardment of southern Lebanon to protect the U.N. observers there.

"Israel would never deliberately target U.N. personnel," Mark Regev said.

According to Regev, Israeli Prime Minister Ehud Olmert called U.N.Secretary-General Kofi Annan and "expressed his regret at this tragedy in Lebanon."

Annan issued a sharply worded statement Tuesday evening which said he was "shocked and deeply distressed by the apparently deliberate targeting ... of a U.N. observer post in southern Lebanon." He called on Israel to conduct "a full investigation into this very disturbing incident."

"This coordinated artillery and aerial attack on a long established and clearly marked U.N. post at Khiyam occurred despite personal assurances given to me by Prime Minister Ehud Olmert that U.N. positions would be spared Israeli fire," Annan said.

"Furthermore, General Alain Pelligrini, the U.N. force commander in south Lebanon, had been in repeated contact with Israeli officers throughout the day on Tuesday, stressing the need to protect that particular U.N. position from attack."

The timeline provided CNN by a U.N. officer in Lebanon showed the first bomb exploded about 200 yards from the U.N. outpost at 1:20 p.m. Tuesday, prompting the first call by the UNIFIL observers to their designated contact with the Israeli military. The officer said they were assured by the Israeli liaison that he would stop the attacks.

A series of about nine more bombs hit within 100 to 400 yards from the observers over the next several hours, with a call to the Israeli military following each explosion.

The U.N. base at Noqoura lost contact with the outpost at 7:40 p.m., apparently the time of the direct hit, the officer said.

China issued a strong condemnation of the Israeli airstrike, according to a statement posted on the Chinese Foreign Ministry Web site Wednesday.

"China urges the concerned sides, especially Israel, to take tangible measures to ensure the security of UN peacekeepers," said Foreign Ministry spokesman Liu Jianchao.

China's state-run news agency -- Xinhau -- said Chinese Assistant Foreign Minister Zhai Jun called in Israeli Ambassador Yehoyada Haim Wednesday morning to discuss the attack.

"China strongly condemns the activity to raid the UN peacekeeping post and urge Israel to carry out thorough investigation and apologize to China and the victim's families and coordinate with China to deal with the aftermath," Xinhau quoted Zhao as telling the Israeli ambassador.

Xinhua said the Chinese observer killed was Du Zhaoyu.

Journalist Anthony Mills in Beruit contributed to this report.

© 2006 CNN.com

###