Mohammed Dahlan has been based in exile in the UAE since falling out with Abbas and being expelled from his Fatah movement.
He has been improving relations with Islamists Hamas to the chagrin of the West Bank-based Abbas.
"Fifteen million dollars will be pumped monthly from the beginning of next month to the Palestinian Joint Liability Committee in support of relief, humanitarian and development projects in the Gaza Strip to alleviate their suffering," Samir Al-Mashharawi, an ally of Dahlan, said in a statement.
Hamas, considered a terrorist organisation by the United States, European Union and Israel, could benefit from increased international legitimacy if it were to formally share control with Dahlan.
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On Friday, Hamas leaders and Dahlan allies again met in Cairo to discuss easing the blockade of Gaza with Egyptian officials.
The Rafah crossing from Egypt has been largely closed in recent years due to disputes between Hamas and Cairo.
Israel has maintained a crippling blockade on Gaza for a decade.
Seeing his two longtime adversaries moving closer, Abbas has sought to weaken Hamas -- reducing electricity funding for the strip and cutting salaries of state employees there.