BAGHDAD — Sunni militants have seized an Iraqi crossing on the border with Syria after a daylong battle in which they killed some 30 Iraqi troops, security officials said Saturday.

The capture of the Qaim border crossing deals a further blow to Prime Minister Nouri al-Maliki’s government, which has struggled to push back against Islamic extremists and allied militants who have seized large swaths of the country, including the second largest city Mosul, and who have vowed to march on Baghdad.

Police and army officials said the Islamic State of Iraq and the Levant and allied militants seized the crossing near the border town of Qaim, about 200 miles west of Baghdad, after battling Iraqi troops all day Friday.

The officials said people were now crossing back and forth freely.

Sunni militants have carved out a large fiefdom astride the Iraqi-Syrian border and have long traveled back and forth with ease, but the control of crossings allows them to more easily move weapons and heavy equipment to different battlefields.

The fall of the border crossing came as al-Maliki faces mounting pressure to form an inclusive government or step aside, with both a top Shiite cleric and the White House strongly hinting he is in part to blame for the worst crisis since U.S. troops withdrew from the country at the end of 2011.

Grand Ayatollah Ali al-Sistani, the most respected voice for Iraq’s Shiite majority, on Friday joined calls for al-Maliki to reach out to the Kurdish and Sunni minorities a day after President Barack Obama challenged him to create a leadership representative of all Iraqis.

Al-Sistani normally stays above the political fray, and his comments, delivered through a representative, could ultimately seal al-Maliki’s fate.

Calling for a dialogue between the political coalitions that won seats in the April 30 parliamentary election, al-Sistani said it was imperative that they form “an effective government that enjoys broad national support, avoids past mistakes and opens new horizons toward a better future for all Iraqis.”

Al-Sistani is deeply revered by Iraq’s majority Shiites, and his critical words could force al-Maliki, who emerged from relative obscurity in 2006 to lead the country, to step down.