Soldiers and the sick cast early votes Thursday ahead of weekend elections that will determine the leadership of Iraq's Kurdish region, which is locked in an increasingly bitter dispute with the central government over oil-rich land. A coalition of the Patriotic Union of Kurdistan and the Kurdistan Democratic Party, two parties that have dominated the self-ruled region for decades, faces a challenge from new opposition alliances that seek to capitalize on complaints about authoritarian conduct and alleged corruption. About 2.5 million eligible voters in the region's three northern provinces - Irbil, Dahuk and Sulaimaniyah - will on Saturday elect their 111-seat parliament and next president. Prison inmates, sick people in hospitals and members of the Kurdish security forces known as “peshmerga” were among those allowed to vote early. “I have the right to vote, to feel no different from anyone outside the prison,” said Nisreen Muhammad, an inmate who voted in a Sulaimaniyah prison. “We all have the same right.” Some Kurds voted in polling stations in cities outside their region. At a voting center in Baghdad, one Kurdish military official joyfully waved a finger stained with the purple ink used to mark ballot papers. The Kurds had hoped to simultaneously hold on Saturday a referendum on a proposed constitution, but national authorities scuttled that plan. The draft constitution lays claim to disputed areas outside the three Kurdish provinces, and Iraqi Arabs view it as an effort to expand Kurdish authority. Tension between Kurds and Arabs, particularly around the oil-rich northern region of Kirkuk, is considered a major threat to Iraqi stability despite big security gains after years of war. In Washington on Wednesday, President Barack Obama pressed Iraqi Prime Minister Nouri Al-Maliki to be more flexible about sharing power and allowing provincial governments a greater role in decision-making. Al-Maliki, who has been accused of trying to gain political capital by playing up sectarian divisions, said his Shiite-led government would work hard to unite Iraq. Iraq's parliament has not yet produced a law outlining as to how Iraq's oil wealth should be divided among the country's religious and ethnic groups, and Kurds seek to sign oil deals with foreign companies without an approval from Baghdad.