Yehoyada Haim expressed the Israeli government's apology for the event, pledging to carry out broad and in-depth investigation to find the truth at an early date.

Chinese Ambassador to the UN Wang Guangya on Wednesday made an emergency call to UN Deputy Secretary-General Mark Malloch Brown, asking the UN to require Israel to take every measure to ensure the security of UN peacekeepers, including those from China, and investigate the event.

The Chinese victim Du Zhaoyu was among the four UN peacekeepers killed in the Israeli air strike Tuesday night.

The other three dead UN observers were from Finland, Austria and Canada, UN Interim Force in Lebanon (UNIFIL) sources confirmed.

Milos Struger, spokesman of the UNIFIL said earlier that an Israeli bomb directly hit the base of the UN Observer Group in the town of Khiam near the eastern end of the border with Israel.

UN Secretary-General Kofi Annan said in a statement that he was "shocked and deeply distressed" by the attack, saying it's "apparently deliberate targeting by Israeli Defense Forces."

In Jerusalem, Israel expressed regret on Wednesday over the deaths of four UN observers in south Lebanon.

"Israel sincerely regrets the tragic death of the UN personnel in south Lebanon," said Israeli Foreign Ministry spokesman Mark Regev.

France and New Zealand condemned the bombing. US Ambassador to the UN John Bolton also expressed regret over the deaths of UN observers.

A total of 180 Chinese officers and soldiers as well as three observers, including Du, were working in Lebanon, as part of the UN peacekeeping mission, according to diplomatic sources.

There are nearly 2,000 UN peacekeeping forces in Lebanon, which were launched in March, 1978 based on UN resolutions.