The Biden administration has yet to find a smoking gun linking Iran directly to planning and executing the attack on Israel this weekend, US officials told CNN on Sunday.

However, there's no denying Iran's history of aiding Hamas, officials said.

"Of course Iran is in the picture," one US official told CNN. "They've provided support for years to Hamas and Hezbollah."

In the immediate aftermath of the attack, senior US officials maintained that it was too early to determine whether Iran had any direct role in planning and supporting Hamas' attack. "It is early" and a matter of direct interest to determine, one senior official said.

But officials are beginning to go as far as to say that Iran's well-established connections to Hamas would mean it is likely Iran helped train and finance efforts that led to this weekend's attack.

"Iran's close ties to Hamas and financial and operational support make it likely they had a role in this," one Democratic senator, who was expected to receive a classified briefing on Monday, told CNN.

But for now, US officials say there is no intelligence making the direct connection.

One congressional source said that given the sophistication of the attack, Iran would have had a role, since Hamas does not have the ability to buy weapons at this scale. The question now: To what extent Iran played a role.

Another key question is how Hamas coordinated and amassed the people and weaponry to execute the operation and did so undetected by key Middle Eastern and Western intelligence operations, including the Israelis.

"In this specific instance, we have not yet seen evidence that Iran directed or was behind this particular attack," Secretary of State Anthony Blinken said on CNN's "State of the Union" on Sunday. On NBC's "Meet the Press" he added, "That's something we're looking at very carefully, and we've got to see where the facts lead."

While the administration has rejected the criticism that a recent deal unfreezing billions of dollars in Iranian funds was connected to the attack, Blinken was more circumspect about whether the deal freed up Iran to spend other money, noting that Iran has long underwritten terrorism.

"Iran has, unfortunately, always used and focused its funds on supporting terrorism, on supporting groups like Hamas. And it's done that when there have been sanctions; it's done that when there haven't been sanctions. And it's always prioritized that," he said on "Meet the Press."