Chief among the questions was whether Washington had any prior warning of the killing of Yassin, who had become increasingly influential in the Palestinian territories but who was dubbed by Israel as the "Palestinian Osama bin Laden."
Both the State Department and the White House criticized Israel's action as "deeply troubling" -- a formulation that fell short of the European Union's condemnation of the killing -- and said the U.S. had no advance warning. Israel also said the United States had no advance knowledge of the attack.
But the assassination of Yassin outside a Gaza mosque yesterday is raising key questions about its possible impact on U.S. policy toward the Israeli-Palestinian conflict, as well as Washington's initiatives in the so-called Greater Middle East.
Despite U.S. denials, the widespread perception among Arabs is that Washington, as Israel's strongest ally, must have approved of the killing beforehand -- or at least looked the other way.
Certainly, Hamas sees it that way. The militant group said yesterday that -- in response to what it believes to be U.S. approval of the action -- it will now directly target the United States.
Henry Siegman is a leading U.S. expert on the Middle East. In an interview with RFE/RL, he says the Yassin assassination has further undermined U.S. credibility in the region, which has already been hampered by unproven allegations on Iraq's weapons programs and its perceived bias toward Israel.
"It's entirely possible that the matter was taken up with the [U.S.] administration by the Israelis," he said. "But had they asked the question -- 'Can we do that?' -- I'm certain even after listening to some of the more compromising statements that were made, that the United States did not say, 'Yes, you can go in.' They probably just didn't respond. And the lack of a response was taken by [Israeli Prime Minister Ariel] Sharon not as a green light [to go ahead] but certainly an orange light [of caution] -- that things might not be too bad if he went ahead."
Siegman, director of the U.S./Middle East Project at the Council on Foreign Relations in New York, says initial U.S. reaction to the killing has helped fuel perceptions that the United States approved of it. Remarks by national security adviser Condoleezza Rice focused on Yassin's ties to terrorism and did not criticize Israel, which McClellan and other U.S. officials later rushed to do -- albeit softly.
And Siegman says that will only hurt American efforts in the region that require Arab goodwill if they are to succeed, such as rebuilding Iraq or a new, controversial U.S. initiative to promote democracy in the Greater Middle East: "A highly problematic initiative that the United States undertook for the Greater Middle East -- the spread of democracy, reform, trade, etc. -- has become even more complicated and less likely [to encounter] a friendly reception."
Siegman -- a longtime director of the American Jewish Congress -- says U.S. efforts to promote the "road map," an internationally backed plan for resolving the Israeli-Palestinian dispute, have also taken a hit. Siegman says the road map always depended on the Palestinian Authority cracking down on militant groups such as Hamas. But its ability to do so now, he says, is virtually nonexistent: "What the assassination has done is powerfully strengthen Hamas and its standing in the Palestinian street. There are few Palestinians today who would dare speak out against Hamas."
But while the killing may have weakened the Palestinian Authority and hampered U.S. efforts on the road map, Washington has given no hint that it will be moved to alter its policies toward the conflict.
At a briefing yesterday, State Department spokesman Richard Boucher said there is no doubt that Yassin's killing will increase tensions in the region and not help the peace process. But when asked whether or not the United States will ask Israel to specifically cease its use of targeted assassinations -- a policy Washington officially opposes -- Boucher was noncommittal.
"We're looking for all the parties to exercise restraint. We're looking for all the parties to do everything possible to avoid actions that can further escalate the tensions in the region. As far as how specific that gets, I just don't know at this point."