Talks with Israel on providing US military assistance are "very much underway," a White House senior official said Saturday, following the surprise large-scale attack by the Palestinian militant group Hamas.

The official indicated an announcement by Washington was possible as early as Sunday, but noted that the situation in Congress -- where the lower chamber currently lacks a leader -- will complicate the matter.

There is "probably is a role for Congress here and without speaker of the House, that is a unique situation we're going to have to work through," he said.