Turkey's Recep Tayyip Erdogan has said US President Joe Biden had "bloody hands" because of his support of Israel in the raging conflict in the Gaza Strip.
Erdogan had spent the past few months trying to mend relations with Washington and reaching out to other Western allies after a year of sharp disputes.
But he lashed out at Biden directly in a furious nationally televised address on Monday.
"You are writing history with your bloody hands," Erdogan said . "You forced us to say this. Because we can not stay silent on this anymore."
Erdogan has gained support across the Middle East by championing the Palestinian cause during his 18-year rule. He last week vowed to rally the world to Gaza's defence.
"Today we saw Biden's signature on weapons sales to Israel," Erdogan said on Monday in reference to US media reports of a new $735m arms shipment approved by the Biden administration.
The arms sale, which Congress was notified of on May 5, a week before the current Israel-Palestinian escalation began, includes Joint Direct Attack Munitions (JDAMs), which are used to turn bombs into precision-guided missiles, according to the newspaper.
Under US law, the administration is required to notify Congress of such sales. Legislators then have 20 days to pass a resolution opposing the sales. Beyond arms sales, the US provides about $3.8 bn in annual aid to Israel. That aid, unlike to other countries, is not conditional on Israel's human rights records, according to Al Jazeera.