WASHINGTON -- The Middle East remains a challenge to U.S. national security interests, as terrorist groups thrive on the region's instability as they try to export violent extremism around the world, the chairman of the Joint Chiefs of Staff said.

''We are not finished with that fight,'' Army Gen. Mark A. Milley told the House Armed Services Committee yesterday.

Milley appeared with Defense Secretary Dr. Mark T. Esper at a hearing on U.S. policy in Syria and the broader region.

Iran also exploits the volatility and asserts itself through malign influence to achieve regional dominance, he added.

The Defense Department adheres to clear goals in the region that are set forth in the National Security Strategy, Milley said:

• A stable and secure Middle East;
• A Middle East that is not a safe haven and breeding ground for violent extremists;
• A Middle East that is not dominated by a nation hostile to the United States; and
• A Middle East that contributes to a stable, global energy market.

The National Defense Strategy provides military objectives to deter destabilizing activities by Iran and violent extremist organizations, the general said. In turn, he told the panel, the National Military Strategy describes how the joint force achieves NDS objectives with five areas of focus:

• Responding to threats;
• Deterring strategic attack, including the proliferation of weapons of mass destruction;
• Deterring conventional attack;
• Assuring allies and partners; and
• Competing below the level of armed conflict.
• Milley gave the committee an overview of DOD's current operations in the Middle East.

In Syria, he said, combined operations with the Syrian Democratic Forces continue toward completing the enduring defeat of ISIS and preventing its reemergence, he said.

Iraq has been an essential partner in defeating ISIS in the region, the chairman said, and the department continues to work by, with and through Iraqi security forces to achieve a secure and stable Iraq that is able to defend itself.

The military strategy in Afghanistan is to continue to deny the nation as a safe haven for terrorist attacks on the U.S. homeland, Milley said. ''That has been our objective since Oct. 7, 2001,'' he added.

The Defense Department also supports the effort to reach a political settlement between the Taliban and the Afghan government in ''an Afghan-to-Afghan effort that ends this war in a responsible way and meets U.S. national security objectives,'' Milley said.

Iran remains the leading state sponsor of terrorism, the general said, and has increased instability in the region through state and proxy actions. In response, he told the House panel, DOD increased its force posture in the response to Iran's recent attacks on Saudi Arabia and its continued acts of aggression and malign influence throughout the region.

''We will maintain the strategic depth of the joint force in the region in order to deter Iran, assure our partners, and if necessary, respond if deterrence fails,'' he said.

In broad terms, Milley said, the military strategy in the Middle East is part of an interagency, international effort to sustain the conditions-based approach.