Kurdish pesh merga fighters take part in weapons training in the grounds of their camp in Irbil, Iraq, on Nov. 3. (Reuters)

Kurdish leaders in Iraq have quietly expanded a request to Washington for sophisticated arms and protective equipment to battle the Islamic State, but American officials have so far rebuffed the appeals out of concerns about defying the Iraqi government, according to Kurdish officials.

The Obama administration’s reluctance to directly arm the Kurdish forces underscores the challenges the United States faces in Iraq, where it is seeking to expand its effort to help Iraqi forces combat militants without upsetting a fragile political balance between the country’s Sunnis, Shiites and Kurds.

A Kurdish official, speaking on the condition of anonymity to discuss official communications, said Kurdish leaders had presented the Pentagon with an expanded request for U.S. equipment, including mine-resistant armored vehicles and technology to counter improvised explosive devices, such as bomb-defusing robots.

The peshmerga, as the militia forces of northern Iraq’s semiautonomous Kurdish region are known, have had some success retaking territory that Islamic State militants seized this summer. But now, Kurdish officials say, the modestly equipped Kurdish force is struggling to respond to the evolving tactics of militants who are increasingly using explosive booby traps and roadside bombs to defend the territory they hold.

“The fighting changed. The style changed,” the Kurdish official said. “We started to ask for heavier military equipment.”

Navy Cmdr. Elissa Smith, a spokeswoman for the Defense Department, said the Pentagon had responded to the new Kurdish request on Oct. 15, promising to review it and urging leaders of the Kurdistan Regional Government (KRG) to coordinate their requests with the Iraqi government in Baghdad.

Smith said that a coalition of countries allied against the Islamic State had already provided more than 2 million pounds of equipment to help the KRG defend its territory. Most of that has gone through the central government in Baghdad, U.S. officials say.

“Support for all of Iraq’s security forces, including Kurdish elements, will be critical to defeating this threat,” Smith said.

But Kurdish officials say the supplies they have received have comprised only light and medium arms, including ammunition, automatic weapons and artillery rounds. They say heavy arms are needed to combat an adversary such as the Islamic State, which seized large quantities of U.S.-made weapons and equipment abandoned by Iraqi soldiers as the militants advanced this summer.

While U.S. officials have led coordination of the international effort to supply the peshmerga, they have not yielded to Kurdish requests for heavier and more sophisticated U.S.-made military gear.

“It has to go through the proper channels,” a State Department official said on the condition of anonymity. “Everything has to be done through the government of Iraq.”

U.S. officials are also leery of establishing a precedent for providing arms to a force such as the peshmerga, which is not commanded by a national government.

The Kurdish request also reflects the changing nature of the fight in Iraq, where U.S. officials say weeks of U.S. and allied airstrikes and sporadic Iraqi military advances have forced the Islamic State to adopt new, defensive tactics. That has included increased reliance on roadside bombs.

The shift is likely to pose new dangers for Iraqi and Kurdish forces. Kurdish military engineers in particular have taken heavy losses as, equipped only with simple wire cutters, they try to defuse bombs or explosive booby traps, the Kurdish official said.

The repeated Kurdish appeals add another layer of complexity to a close but fraught U.S.-Kurdish relationship. While the United States supported the Kurds’ bid to attain self-governance after the 1991 Persian Gulf War, U.S. officials say the Kurds have overplayed their hand this year by using the Islamic State threat to advance their ambitions for full independence from Iraq.

Rather than sending the Kurds weapons directly, the Obama administration is urging Kurdish leaders to work with the government of new Iraqi Prime Minister Haider al-Abadi. U.S. officials also point to unprecedented military cooperation, brought on by the severity of the Islamic State threat, between the peshmerga and the Iraqi army commanded from Baghdad.

For the time being, Kurds say that history makes them skeptical about promises of new security cooperation from Iraq’s Arab leaders.

Michael Knights, a fellow at the Washington Institute for Near East Policy, said increased cooperation between Baghdad and Irbil, the capital of Iraqi Kurdistan, was critical to the U.S. strategy in Iraq.

“The U.S. government is still working to maximize the chance of a Baghdad-KRG deal on a range of issues including revenue-sharing, joint exports from the Kirkuk oil field, and Baghdad funding and arming of the peshmerga through a new national guard,” he said, referring to some of the long-running disputes between Iraqi Kurds and Baghdad.

“If the U.S. bypasses Baghdad, it undermines one reason for the KRG to continue those negotiations.”

Kurdish forces may soon get at least some of the specialized gear they desire. Canada has promised to provide bomb-defusing robots, although Kurdish officials say that equipment will not arrive until the end of the first quarter of 2015.