BRUSSELS, Feb 19 (Reuters) - All European Union countries except Hungary warned Israel on Monday against launching an offensive in Rafah that they said would deepen the catastrophe of some 1.5 million refugees crammed into the city on the southern edge of Gaza.

"An attack on Rafah would be absolutely catastrophic ... it would be unconscionable," Ireland's Foreign Minister Micheal Martin said before a meeting of foreign ministers from the 27 EU member states in Brussels.

After the talks ended, all but one of them called in a joint statement for "an immediate humanitarian pause that would lead to a lasting ceasefire, the unconditional release of all hostages and the provision of humanitarian assistance".

The statement was issued in the name of "Foreign Ministers of 26 Member-States of the European Union" and diplomats said Hungary - a close ally of the Israeli government - was the sole country that did not sign up.

"We ask the Israeli Government not to take military action in Rafah that would worsen an already catastrophic humanitarian situation and prevent the urgently needed provision of basic services and humanitarian assistance," the ministers said.

Israel is preparing to mount a ground invasion of Gaza's southernmost city, which it has called a last bastion of Hamas control after nearly five months of fighting.

Israel accuses Hamas fighters of hiding among civilians, something the militant group denies, and says "extraordinary measures" were being taken to avoid civilian casualties.

But EU foreign policy chief Josep Borrell said it would be impossible to prevent civilian deaths.

"We have to continue putting pressure on Israel to make them understand that there are so many people in the streets of Rafah, it will be impossible to avoid civilian casualties," he said.

"This, certainly, will be against the respect of humanitarian law."

German Foreign Minister Annalena Baerbock also called on Israel to respect humanitarian law, but said that Israel had the "right to self-defence" as it was clear that Hamas fighters were still operating from Rafah.

"The most important thing would be that Hamas would lay down its weapons," she said.

"Over a million people went to the south of Gaza because the IDF (Israel Defence Forces) told them so. They can't just disappear in the sky."

Photo from Reuters