Militant group able to move weapons and equipment as fighters prepare for likely assault on Baghdad, say officials

The Islamic extremist group Isis has taken a crossing on the Iraq-Syria border 200 miles west of Baghdad, allowing them to move both men and heavy equipment freely, security officials have said.

After a day-long battle on Friday, during which 30 Iraqi troops were reportedly killed, the terrorist group and allied Sunni militants gained control of the crossing near the border town of Qaim, Associated Press reported police and army officials as saying.

The fighters have carved out a large fiefdom astride the border and have long travelled back and forth with ease, but the control of crossings allows them to bring up heavier weapons to different battlefields as they vow to march on Baghdad.

But, according to reports, Sunni gunmen who have fought together to capture large parts of Iraq have also turned their weapons on each other in recent days. There have been clashes between the former allies in Kirkuk province, costing 17 lives, sources told AFP on Saturday.

The agency reported that the fighting erupted on Friday evening between Isis militants and the Army of the Men of the Naqshbandiyah Order (JRTN) in Hawija. There were differing accounts as to what sparked the firefight.

One security official said that JRTN fighters had refused an Isis demand to give up their weapons and pledge allegiance to the jihadist force. Witnesses, however, told AFP the two sides clashed over who would take over multiple fuel tankers in the area.

Experts have questioned how long the alliance of Sunni insurgent groups, who are led by Isis but also include others, can hold together given their disparate ideologies. "If history repeats itself, then Isis, because it's got a transnational goal of a caliphate, because it's radical, because it's got this ludicrously absurd … approach to Islam, they can't help but break that coalition," said Toby Dodge, head of the Middle East centre at the London School of Economics.

Nevertheless, the capture of the Qaim border crossing deals a further blow to Iraq's embattled prime minister, Nouri al-Maliki, after the country's highest Shia authority, Ayatollah Ali al-Sistani, called on Friday for the quick formation of a new and "effective" government.

Maliki's government has struggled to push back against Isis and its allies who have seized large swaths of the country, including the second largest city Mosul. He is coming under increasing pressure to form an inclusive government or step aside in the face of deepening divisions between Iraq's Sunni, Shia and Kurdish communities.

Both a top Shia cleric and the White House have strongly hinted they believe him to be in part to blame for the worst crisis since US troops withdrew from the country at the end of 2011.

Calling for a dialogue between the political coalitions that won seats in the 30 April parliamentary election, 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."

His call to defend the country has given the fight against the Sunni insurgents the feel of a religious war, but his office in Najaf dismissed that charge, saying the top cleric was addressing all Iraqis.

However on Friday, hundreds of black-clad Shia militants, members of the newly formed "Peace Brigades," marched in the Shia holy city of Najaf, heeding a call to defend holy sites by Shia cleric Moqtada al-Sadr, AP reported. Sadr once led a powerful militia that battled US troops and was blamed for attacks on Sunni civilians during the height of the country's sectarian bloodletting in 2006 and 2007.