Kurdish forces, backed by US air power, have been holding out for weeks against an IS offensive around Kobane, which has become a high-profile symbol of efforts to stop the advance of the jihadists.
The Kurdish regional government in northern Iraq unveiled plans on Friday for up to 200 well-trained peshmerga to join Syrian Kurdish forces defending Kobane in the coming week.
Kurdish news agency Rudaw said the first contingent could head to the town as early as Sunday, but there was no immediate confirmation of that timetable.
Since Turkey conceded to US pressure to allow vetted reinforcements into Kobane to prevent IS winning the prominent battle for the town, the jihadists have made repeated attempts to cut the border before any help can arrive.
Before dawn on Saturday, IS fighters hit Kurdish forces defending the Syrian side of the border crossing with mortar and heavy machinegun fire, an AFP correspondent on the Turkish side reported.
The heavy mortar fire around the Mursitpinar crossing prompted the Turkish army to order the evacuation of nearby hilltops from where the world's press has been watching the battle for the town.
The US-led military coalition fighting IS launched 22 air strikes in Iraq and one in Syria on Friday and Saturday, the Pentagon said.
Eleven of the bombings in the heavy barrage targeted IS units, buildings, positions and vehicles near Iraq's strategic Mosul Dam.
Advance guard ready
Kurdish forces backed by US air strikes on Saturday retook the town of Zumar northwest of Mosul from IS after weeks of fighting, a senior officer said.
IS still holds significant areas in northern Iraq and elsewhere in the country, as well as swathes of neighbouring Syria.
The Kurdish news agency said an initial peshmerga contingent of 150 was ready to leave for Kobane and would be headed by Sihad Barzani, brother of Iraqi Kurdish regional president Massoud Barzani and head of its artillery brigade.
It cited peshmerga officials as saying that an additional 1,000 Iraqi Kurdish fighters would follow.
Rudaw quoted a senior peshmerga officer as saying that the Iraqi Kurdish forces would deploy with heavy weapons, but that undertakings had been given to both Ankara and Washington that they would not be handed over to Syrian Kurdish forces.
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"Our enemies in Kobane are using heavy weapons and we should have heavy weapons too," he said.
The main Syrian Kurdish fighting force in Kobane has close links with the outlawed rebel Kurdistan Workers Party (PKK), which has fought a three-decade insurgency in southeastern Turkey.
Ankara has been adamant that no heavy weaponry should fall into its hands.
Turkey has tightly controlled the flow of both fighters and weapons to Kobane, and has accepted only Iraqi Kurdish or Syrian rebel reinforcements for the town.
Washington delivered light weapons to the town's Kurdish defenders last weekend, but was forced to do so by air after Ankara refused deliveries by land.
The Turkish government has been one of the leading supporters of the rebel Free Syrian Army (FSA) in its more than three-year civil war with the Damascus regime, and has proposed allowing in 1,000 of its fighters into Kobane.
But Syrian Kurdish officials inside the town have expressed reservations about the Turkish plan, saying that any deployment must have their approval and that FSA forces would be better used opening new fronts against IS elsewhere.
Washington has expressed new confidence that Kobane's fall to IS can be averted, but has cautioned that in neighbouring Iraq a major fightback against the jihadists is still months off.
Iraqi government forces have come under renewed attack by IS south of Baghdad, with troops battling on Saturday to secure the route used by hundreds of thousands of Shiite pilgrims headed for the shrine cities of Najaf and Karbala.
Eight soldiers were killed in the assault by IS militants which began in the Jurf al-Sakhr area on Friday, officers said.
Senior US administration officials and military commanders acknowledged in recent days the Iraqi army is months away from any sustained counter-offensive that could roll back the IS from its strongholds in Iraq's western and northern provinces.
Pilgrims taking part in Ashura commemorations, which mark the death of Imam Hussein, one of the most revered figures in Shiite Islam, are often targeted with bombings during the annual rituals, which take place this month.
But this year's march to Karbala is set to be more dangerous than most, with militants from IS holding territory along the way.