BAGHDAD — The Kurdish regional government responded Thursday to harsh criticism from Iraq’s prime minister, Nuri Kamal al-Maliki, announcing that its ministers would boycott cabinet meetings, demanding an apology to the Iraqi people and calling on Mr. Maliki to step down.

The political fissure was exacerbated after Mr. Maliki on Wednesday accused the Kurds of turning their regional capital into the headquarters of the Islamic State in Iraq and Syria, as well as harboring members of the Baath Party of former President Saddam Hussein and other opponents of the Iraqi government.

The Iraqi government halted all cargo flights to Kurdistan on Thursday, said Capt. Nasser al-Bandar, the head of civil aviation in the Iraqi government. Kurdistan had responded by halting its cargo flights to Baghdad, he said.

Iraq has also notified the United Nations that Sunni militants from ISIS seized nuclear material from a university in the northern city of Mosul last month as they advanced toward Baghdad, the nuclear regulatory body of the United Nations said Thursday.