"According to our information, Iran has played a big role in what happened in Gaza," al-Tirawi told a news conference.
"Dozens of members of Hamas have been trained in Iran, and Hamas smuggled in weapons through tunnels not to fight Israel but against the Palestinian Authority."
He said that the "plan" had been "carried out in coordination with Iran, and Iran has been informed of every step".
Fawzi Barhoum, spokesman for the Hamas movement, responded to the accusations by saying that al-Tirawi was engaging in "media fabrications, lies, attacks on Hamas and attacks on the Palestinian national project".
He said that Hamas had evidence that al-Tirawi and others had "worked with the Israeli occupation authorities to destroy Hamas".
Ahmed Abul Gheit, Egypt's foreign minister, last week accused Iran of having encouraged Hamas to seize the Gaza Strip, but al-Tirawi's comments were the first time that a senior Palestinian official has blamed Iran.
Iran surprised
Iran denied Abul Gheit's accusations.
Mohammad Ali Hosseini, Iran's foreign ministry spokesman, said it was "surprising some Arab countries ignore the Western countries, the United States and the Zionist regime".
He said Iran "had the most responsible approach" towards the Palestinians.
Iran has said in the past that it does support Palestinian groups resistant to Israel, but does not arm or train their fighters.
Hosseini said Iran supports Hamas "politically and spiritually" and that the "humanitarian aid would be provided through channels that it benefits all Palestinian people".
Mahmoud Abbas, the Palestinian president, had previously accused "foreign elements from the region" of orchestrating Hamas's takeover of Gaza.
Abbas earlier sacked Brigadier Suleiman Khodr, the military commander at the time that Fatah was pushed from the Gaza strip, demoting him to the rank of a simple soldier.