Iraqi families displaced by fighting in their home towns receive humanitarian aid at the Khazir refugee camp, near Erbil, northern Iraq, 23 July 2014. (Kamal Akrayi/EPA)

The writer was the U.S. ambassador to Iraq from 2005 to 2007 and U.S. ambassador to the United Nations from 2007 to 2009.

During the past few days, the extremist group known as the Islamic State has made significant advances. After consolidating its gains since the fall of Mosul and other Sunni areas, the group sought to move toward Baghdad. For now, that advance has been blocked by Shiite militias, what remains of the Iraqi forces and assistance from Iran and the United States. It is evident, however, that the Islamic State has amassed enough manpower and resources to move against the Kurdish region. Its recent attempt to take over the Mosul dam as well as its seizure of the city of Sinjar and the other areas controlled by the Kurds, who were overwhelmed by a force using superior U.S. equipment captured from the Iraqi army, could have devastating effects.

Should it capture and control the Mosul dam — Iraq’s largest — the Islamic State would hold hostage the precious water supply of millions of Iraqis. If it decided to destroy the dam, it could put people as far south as Baghdad at risk of deadly flooding. Just the threat of doing so would give the extremists much leverage.

The humanitarian tragedy is also worsening by the day. The United Nations estimates that the capture of Sinjar may have displaced 200,000 civilians. Hundreds of families have taken refuge without water and food in the Sinjar mountains. Without urgent assistance, they face the choice of submitting to the extremists’ version of Islam or perishing. The Islamic State has also taken over new areas with significant oil fields, and its latest advances demonstrated the weaknesses of Kurdish pesh merga forces in terms of weapons, munitions and logistics. These recent developments suggest that the group is gaining strength and consolidating control in areas it occupies.

The United States has reacted by authorizing the direct supply of munitions to the Kurds and, with Baghdad’s agreement, the shipment of some Foreign Military Sales (FMS) program weapons to the Kurds. It is also coordinating Iraqi air attacks against Islamic State targets relevant to the defense of the Kurdish region. Similarly, Washington has arranged and coordinated an Iraqi humanitarian air drop for those in the mountains. These are positive steps. If sustained, they have the potential to improve strained relations between Baghdad and Irbil.

However, the Kurdish regional government and the Iraqi government urgently need more substantial assistance.

First, there is a pressing need to provide humanitarian aid to the civilians displaced by the fighting in Sinjar. Many could die of thirst and hunger in a matter of days. To supplement the limited Iraqi effort, the United States may have to consider organizing its own air drops of supplies. This would need to be followed by a larger program to assist the Christians and Muslims who have fled other areas seized by extremists.

Second, the United States needs to reconsider its thinking on the timing of security assistance. There are different views on how Washington should sequence additional assistance to the Iraqis, including direct U.S. attacks on Islamic State targets. One view is that the United States should condition such support on the selection of a new prime minister and the formation of a broadly accepted unity government in Baghdad. There was merit to this logic before the Islamic State’s recent gains, but now the threat is escalating so fast that waiting could have catastrophic consequences. Irbil, Baghdad and Mosul are operating on a different timeline than Washington.

Given the great expansion of the threat, U.S. support should be expedited. The United States should move immediately to work with local forces opposed to the Islamic State — not just the government in Baghdad but also Sunni Arabs and the Kurds. Washington is open to the idea, according to testimony by Deputy Assistant Secretary of State Brett McGurk before the Senate last month; it should urgently implement it. In particular, the United States can play a key role in expediting the provision of ammunition and training, operational advice and coordination among these local forces and some of Iraq’s concerned neighbors.

Last week, the governor of Mosul raised this point when he announced the formation of an anti-Islamic State force in and around Mosul. Several Sunni groups have sought U.S. support. But Washington has been reluctant to assist them pending the formation of a new government. The Kurdish regional government, too, has pleaded for security support, with little response until now. Now that the United States is moving on the Kurdish front, it needs to make a similar move and offer support for appropriate Sunni groups.

Third, Washington should consider military measures that would degrade the Islamic State’s ability to threaten others. This could come in the form of U.S. airstrikes by unmanned or even manned platforms against Islamic State camps and supply routes. Like the Taliban in Afghanistan in 2001, the Islamic State is vulnerable to air power. Such attacks would also have a positive psychological effect on the morale of the pesh merga, the Iraqi army and Sunni Arabs fighting the extremists.

The situation in Iraq is extraordinarily urgent. The Islamic State has become a lethal and capable military force with control over oil fields and infrastructure critical to all of Iraq. It recruits from around the world, and it poses a threat to vital U.S. interests in Iraq, the Middle East and, potentially, the U.S. homeland. To contain, reverse and defeat it requires adjusting our plans based on developments on the ground. Now is the time to do so.