Palestinian President Mahmoud Abbas has expressed regret for a shooting incident involving the Palestinian prime minister that killed his bodyguard.

Hamas officials have accused Mr. Abbas' presidential guard of attacking Prime Minister Ismail Haniyeh's traveling party near the Egyptian border crossing in Gaza Strip. The guard has denied the charge, but the incident is likely to heighten tensions between the rival Palestinian Fatah and Hamas factions.

Hamas says at least 20 people were wounded in the firefight Thursday, including Mr. Haniyeh's son. The battle erupted after Israel allowed the prime minister to return to the Gaza Strip after he left millions of dollars in aid behind.

Israeli officials said they closed the Rafah border crossing to prevent Mr. Haniyeh from returning with money he raised during a tour of Muslim nations.

Western officials say he was in possession of $35 million. Media reports say he left the money in Egypt.

Earlier Thursday, angry Hamas supporters stormed the border terminal to protest the border closure. Several people were wounded.

Fatah and Hamas are locked in a power struggle. Hamas won legislative elections in January. Fatah still controls the presidency.

Some information for this report was provided by AP and Reuters.