WASHINGTON (Reuters) - The White House on Tuesday provided the most complete definition yet of what it considers a "major ground operation" in Rafah that could trigger a change in United States policy toward Israel, and said Israel's actions there have not yet reached that level.

"We have not seen them smash into Rafah - we have not seen them go in with large units, large numbers of troops in columns and formations in some sort of coordinated maneuver against multiple targets on the ground. That is a major ground operation. We have not seen that," White House national security spokesperson John Kirby told reporters at a briefing.

Israel's three-week-old Rafah offensive stirred renewed outrage and prompted an outcry from global leaders after an airstike on Sunday that Gaza officials said killed at least 45 people when a blaze ignited in a tent camp in a western district.

The Biden administration has repeatedly warned Israel against launching a large-scale military offensive in Rafah, a city in southern Gaza packed with refugees who followed Israel's previous orders to evacuate there. President Joe Biden himself publicly warned Israel this month that the U.S. would stop supplying it with weapons if Israeli forces conduct a major invasion there without a credible plan to protect civilians.

Israel told around one million Palestinian civilians displaced by the almost eight-month-old war to evacuate to Al-Mawasi when it launched its incursion in Rafah in early May. Around that many have fled Rafah since then, the U.N. agency for Palestinian refugees UNRWA reported on Tuesday.

Asked about reports that Israeli forces have moved into central Rafah, Kirby said "my understanding is, and I believe the Israelis have spoken to this, that they are moving along something called the Philadelphia corridor, which is on the outskirts of the town, not in the town proper."

"We have not seen a major ground operation and these tanks are moving along a corridor that they have told us previously that they would use on the outskirts of the town to try to put pressure on Hamas," Kirby said.

The World Court last week ordered Israel to immediately halt its military assault on Rafah, in a landmark emergency ruling in South Africa's case accusing Israel of genocide.

Israel said it had targeted two senior Hamas operatives in a compound and had not intended to cause civilian casualties.

"I don't know how anybody could dispute that they were trying to go after Hamas in a targeted precise way," Kirby said, adding that the U.S. would wait for the results of Israel's investigation into the incident.

The U.S. is by far the biggest supplier of weapons to Israel, and it accelerated deliveries after the Oct. 7 Hamas-led attacks.

Rafah was a major entry point for humanitarian relief before Israel stepped up its military offensive on the Gaza side of the border earlier this month and seized control of the crossing from the Palestinian side.

More than 36,000 Palestinians have been killed in Israel's offensive, Gaza's health ministry says. Israel launched its air and ground war after Hamas-led militants attacked southern Israeli communities on Oct. 7, killing around 1,200 people and seizing more than 250 hostages, according to Israeli tallies.

(Reporting by Trevor Hunnicutt; Writing by Katharine Jackson. Editing by Heather Timmons and Josie Kao)

By Trevor Hunnicutt and Katharine Jackson