UNITED NATIONS — America’s blocking of a condemnation of Israel at the Security Council will make it hard to agree how to defuse Iran’s nuclear threat, China said yesterday.

The council debated for two days whether Israel should be “condemned” or “deplored” for the deaths of four U.N. observers in southern Lebanon on Tuesday. Nevertheless, it is expected early next week to demand that the force of 2,000 unarmed blue helmet troops will remain in the war zone.

Although Secretary-General Annan said the United Nations Interim Force in Lebanon is “impeded” from fulfilling its poorly defined mission, he recommended that the council leave the troops stationed in remote Lebanese posts, like the one in Khiyam, where four unarmed observers from China, Austria, Finland, and Canada were killed Tuesday by Israeli fire.

The Israeli ambassador to the United Nations, Dan Gillerman, told reporters another attack took place yesterday on a UNIFIL post, this time by Hezbollah. The attack went unreported by the United Nations, and spokesmen declined to confirm the report.

According to yesterday’s statement, the council was “deeply shocked and distressed” that the Israel Defense Force had fired on a U.N. observer post. America rebuffed China’s attempt to include a “deliberate attack against U.N. personnel” in the statement, however, and it was omitted from the text.

Mr. Annan’s call for a U.N.-Israeli “joint investigation” was blocked. Mr. Gillerman said Israel’s justice system did not need outside support. The statement called on Israel to “take into account” U.N. material when conducting a “comprehensive inquiry.”

“The working relations on this particular issue will have its impact on the working relations on other issues,” China’s ambassador to the United Nations, Wang Guangya, told reporters. He added that China maintains its opposition to dealing with Iran’s nuclear issue at the Security Council.

The council is expected to take up the Iranian issue as early as Friday. According to European and American diplomats, the five permanent members are either “very close” to an agreement that would make uranium suspension mandatory, or have reached such an agreement. Nevertheless, Mr. Wang’s statement indicated that several issues remained unresolved.

On Monday, the council is expected to pass a French-proposed resolution adopting Mr. Annan’s request to extend the mandate of UNIFIL for a month.

Prime Minister Harper of Canada cast doubt yesterday on Mr. Annan’s assertion that Israel targeted the UNIFIL post deliberately. “I certainly doubt that to be the case,” he said.

Mr. Harper called for an investigation, but said he wanted to know why the post — where one Canadian observer was killed — “remained manned during what is now, more or less, a war.”

Asked why the council is not pulling UNIFIL troops out of the war zone, Mr. Wang told the Sun, “I think it is up to the Secretariat.” When told the Secretariat maintained the decision was the council’s, Mr. Wang said, “So maybe, I think, there has to be consultation and coordination between the council and” the peacekeeping department.