The Pentagon confirmed about 50 military personnel were at Al-Asad air base to prepare the way for a larger contingent of advisers and trainers to assist Iraqi security forces.
President Barack Obama has announced plans to double the number of American troops in Iraq to up to 3,100 as US-led efforts against the extremists enter what he called a "new phase".
Parts of mainly Sunni Anbar province have become a stronghold for IS, which has seized control of major parts of Iraq and Syria, and some of Baghdad's forces who were hard-pressed by the extremists fell back to Al-Asad air base.
The sprawling desert airfield was hub for American troops and aircraft from 2003 to 2011.
A string of battlefield defeats for Iraqi forces in Anbar has led to warnings that the province, which stretches from borders with Syria, Jordan and Saudi Arabia to the western approach to Baghdad, could fall entirely.
Some of Anbar's powerful tribes are battling the extremist group, and have played an important role in keeping more of the province from falling.
Parliament speaker Salim al-Juburi visited tribal leaders from Anbar at Al-Asad base on Tuesday to "raise morale" and "urge the government to (provide) a large amount of... weapons and equipment to face the danger of terrorism," he told AFP.
Sheikh Ashur Jabr Hamadi, one of the tribal leaders at Al-Asad, said the lack of ammunition was a problem, but the "most important thing we need is air cover".
"We request the coalition countries to give us air cover -- so far it is very weak."
Washington has forged an alliance of Western and Arab nations to take on IS and launched a barrage of air strikes against it in Syria and Iraq.
One of the strikes on Friday was reported to have hit a gathering of IS leaders but there has been no confirmation of reports IS chief Abu Bakr al Baghdadi was wounded or killed.
US officials have insisted the mission will not see American troops engage in combat and are instead pushing for local forces to tackle IS on the ground.
For Syria, the United States has approved plans to train 5,000 recruits from among moderate rebel forces battling President Bashar al-Assad, but Washington came under fire Tuesday for having a "confused" strategy.
The leader of the moderate Syrian opposition, Hadi al-Bahra, said no strategy to target the extremists would work as long as Assad remains in power.
"The coalition is fighting the symptom of the problem, which is ISIS, without addressing the main cause, which is the regime," Bahra told The Guardian newspaper, using another name for IS.
"The whole operation has been confused. Air strikes will not be able to win the battle against extremism. You have to defeat ISIS on the ground," said Bahra, who heads the National Coalition.
"And you have to deal with the main cause and source of extremism, which is the regime itself."
After meeting Bahra on Monday, British Foreign Secretary Philip Hammond promised London would make "a significant contribution" to equip and train the moderate opposition.
Kurds fighting IS in Kobane made advances Tuesday in the south of the Syrian town on the border with Turkey, said the Syrian Observatory for Human Rights.
Syrian Kurdish chief Saleh Muslim said his forces were advancing "street by street" and would "recapture the town in a very short time".
The battle against IS has overshadowed the civil war in Syria, where more than 195,000 people have been killed since the start of an uprising in March 2011.
The UN is now pushing a plan for what envoy Staffan de Mistura calls a fighting "freeze" in limited areas.
Assad has said he is ready to consider such a plan for Syria's second city Aleppo, and on Tuesday de Mistura said his government had responded with "constructive interest".
But the rebel Free Syrian Army effectively rejected the freeze, and set virtually impossible-to-achieve conditions.
The UN refugee agency said meanwhile it had been forced to slash the number of people it can help prepare for winter in Syria and Iraq for lack of funds.
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The Arab spring was a big joke .