BAGHDAD — The struggle between the leadership of Iraq and the country’s Kurdish minority intensified Friday, as the Kurds seized two oil-production facilities in Kirkuk province and the prime minister appointed a temporary replacement for the foreign minister.

The ethnic tensions escalated at the same time as reports surfaced of more sectarian violence, notably abductions and killings of Sunnis in central Iraq, and two bombings in Kirkuk. A report released by Human Rights Watch reported that 255 Sunni prisoners had been executed since June 9. The Iraqi government called the report “unfair and inaccurate.”

The oil-production facilities in Kirkuk province, on the border of the Kurds’ semiautonomous region in the north, were seized by Kurdish peshmerga forces early Friday. The complexes were previously run by the government and had a primarily Arab staff. The Arab employees were asked to leave, according to Iraq’s oil ministry and witnesses in Kirkuk.

“These two are among the main wells producing oil in Iraq,” said Assem Jihad, the Oil Ministry spokesman. “They are the spine of Iraq’s oil wealth and produce 400,000 barrels a day.”

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Oil-industry publications said they had produced a little less than half that in recent months, but nonetheless represent a significant share of Iraq’s oil production. In 2012, Iraq produced on average of 3 million barrels of oil a day, according to the Organization of Petroleum Exporting Countries.

“Half of this production goes to the local market, and the other half goes for export,” said Jihad, criticizing the Kurds’ seizure of the field as a “constitutional breach” and “violation of Iraq’s sovereignty.”

In Baghdad, Prime Minister Nouri al-Maliki, a Shiite, replaced the foreign minister, Hoshyar Zebari, a Kurd, with Hussain al-Shahristani, a Shiite from al-Maliki’s bloc. Al-Maliki was responding to a decision by Zebari and other Kurdish Cabinet members to boycott Cabinet meetings to protest al-Maliki’s searing criticism of the Kurds this week.

In a televised address Wednesday, al-Maliki charged that the Kurds were harboring Sunni militant opponents of the central government.

The replacement of Zebari infuriated the Kurds, but it also appeared to solidify their resolve to move ahead with the constitutional procedure to select a new government, including a president, prime minister and Parliament speaker.

“With this step, the prime minister doesn’t leave any room for power sharing,” said Faleh Mustapha, who serves as the foreign-affairs minister for the Kurdish regional government, a separate position from that of Iraqi foreign minister. “Had our ministers resigned from the government, or if we had withdrawn entirely from the government, it would be different, but we are still participating in the political process,” he said.

The Kurds and Baghdad have feuded for years over oil resources, disputed territory and other issues. Yet, they have also found room for compromise, and the Kurds have provided critical backing to help al-Maliki become prime minister.

But their ties are unraveling as the country fragments in the face of the Sunni militant blitz, led by the Islamic State extremist group. The country is effectively being cleaved along ethnic and sectarian lines: the swath of Sunni areas controlled by the Islamic State; the Shiite-majority south and center ruled by the Shiite-led government in Baghdad; and the Kurdish north.

Iraq has a caretaker government because of delays, first in finalizing the election and then because lawmakers have been unable to agree on candidates to fill the top positions. Although it is not stated in the constitution, the speakership typically goes to a Sunni, the presidency to a Kurd and the prime minister slot to a Shiite.

Parliament is scheduled to try again Sunday to name a speaker, which would be the first step toward forming a government.

The Kurds, meanwhile, also find themselves fighting the Sunni militants across the northern front. On Friday, a suicide bomber blew himself up at a peshmerga checkpoint outside Kirkuk, killing 13 people and wounding 23, police and hospital officials said on condition of anonymity because they weren’t authorized to brief the media.

Material from The Associated Press is included in this report.