BAGHDAD (AP) — Iraq’s ruling Shiite and Kurdish blocs have made a key concession to a large group of Sunni Arab legislators in hopes of securing a big majority in a parliamentary vote on a U.S.-Iraqi security pact, a senior Shiite lawmaker and a close aide to the prime minister said Wednesday.

The proposed deal would let American troops stay in Iraq through 2011, meeting a longtime Iraqi demand for a clear timetable for their exit.

But the intensity of political maneuvering among Iraqi factions contributed to deep uncertainty about the outcome of a vote scheduled for Wednesday that will determine the status of 150,000 troops in Iraq after years of war.

Lawmakers planned to vote in a session beginning at 7 a.m. EST, but past meetings have often been delayed.

Prime Minister Nouri Al-Maliki’s ruling coalition appears to be assured of at least a slim majority in the 275-seat legislature. But the prime minister seeks a bigger win that transcends Iraq’s factionalism and sectarian divisions and reinforces the legitimacy of the pact, which could lead to full Iraqi sovereignty and close the bloody chapter that began with the U.S.-led invasion in 2003.