By Nidal al-Mughrabi and Crispian Balmer

CAIRO/JERUSALEM (Reuters) -At least 20 Palestinians were killed on Wednesday at an aid distribution site run by the Gaza Humanitarian Foundation, in what the U.S.-backed group said was a crowd surge instigated by armed agitators.

The GHF, which is supported by Israel, said 19 people were trampled and one fatally stabbed during the crush at one of its centres in Khan Younis in southern Gaza.

"We have credible reason to believe that elements within the crowd – armed and affiliated with Hamas – deliberately fomented the unrest," GHF said in a statement.

Hamas rejected the GHF allegation as "false and misleading", saying GHF guards and Israeli soldiers sprayed people with pepper gas and opened fire.

GHF said Hamas' account was "blatantly false".

"At no point was tear gas deployed, nor were shots fired into the crowd. Limited use of pepper spray was deployed, only to safeguard additional loss of life," GHF said in a written response to Reuters via e-mail.

"Today’s incident is part of a larger pattern of Hamas trying to undermine and ultimately end GHF. It is no coincidence that this incident occurred during ceasefire negotiations, where Hamas continues to demand that GHF cease........

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