Officials said Mr. Sullivan’s remarks reflected the intelligence collected so far, which did not point to direct involvement by Iran.

“We have said since the beginning: Iran is complicit in this attack in a broad sense because they have provided the lion’s share of the funding for the military arm of Hamas,” he said. “They have provided training, they have provided capabilities.”

President Biden is facing fierce criticism from some members of the Republican Party, including candidates for president, who accuse the administration of being soft on Iran. The Biden administration has been trying unsuccessfully to revive a nuclear deal with Iran and recently negotiated a deal for the release of prisoners. In exchange, Iran gained access to $6 billion in frozen oil revenues for humanitarian purposes.

Former President Donald J. Trump and other Republicans tried to cast blame on Mr. Biden, saying that those funds helped to finance the assault. But that $6 billion is not U.S. taxpayer money, as Mr. Trump and others falsely stated. Nor is there evidence that the money, which officials have said is subject to Treasury Department oversight, was used to finance the attacks.

Treasury Secretary Janet L. Yellen did not rule out the possibility of reversing a decision made last month to unfreeze the $6 billion in Iranian funds if it is determined that the country was involved in the attack by Hamas. Ms. Yellen said the funds had not yet been touched.

The United States moved an aircraft carrier to the region, a step meant to deter Iran or its proxies from opening another front in the wake of the assault.