The US does not believe Israel has launched a full-scale invasion of Rafah in southern Gaza, White House spokesman John Kirby has said.
He spoke hours after Israeli forces reached the centre of the city and reportedly seized a strategically important hill overlooking the nearby border with Egypt.
US President Joe Biden said this month he would limit weapons supplies to Israel if it entered the “population centres” of Rafah, where hundreds of thousands of civilians are still believed to be sheltering.
Mr Kirby was also questioned about an Israeli strike and a resulting fire that killed at least 45 Palestinians – many of them women, children, or elderly – at a camp for displaced people on Sunday.
Israel has said the strike targeted and killed two senior Hamas officials, and that it believes the fire could have been caused by an explosion at a Hamas weapons store nearby.
Speaking to reporters, Mr Kirby described images from the aftermath of the strike as “heartbreaking” and “horrific”.
The US state department said it was watching closely for the Israeli military to conduct a quick and thorough investigation into the strike.
Pressed by BBC correspondent Tom Bateman on whether previous such investigations had led to accountability, state department spokesman Matthew Miller declined to name specific cases.
Israel has insisted it will not be able to achieve victory in its seven-month war against Hamas in Gaza without taking Rafah and rejected warnings of catastrophic humanitarian consequences.
The Israel Defense Forces (IDF) first began what it called “targeted” ground operations against Hamas fighters and infrastructure in the east of Rafah on 6 May.
Since then, tanks and troops have gradually pushed into built-up eastern and central areas while also moving northwards along the 13km (8-mile) border with Egypt.