Flying in from Jordan on a visit which the State Department had sought to keep secret amid security concerns, Kerry met Prime Minister Nuri al-Maliki and was to hold talks with Iraqi leaders across the political and communal spectrum.
Kerry "will discuss US actions underway to assist Iraq as it confronts this threat from ISIL and urge Iraqi leaders to move forward as quickly as possible with its government formation process to forge a government," State Department spokeswoman Jen Psaki said ahead of the meetings.
Iraqi security forces are struggling to hold their ground in the face of an insurgent onslaught that has seized major areas of five provinces, displaced hundreds of thousands of people and sparked fears that the country could be torn apart.
Maliki's security spokesman said today that "hundreds" of Iraqi soldiers have been killed since the insurgents launched their offensive on June 9. The announcement on television by Lieutenant General Qassem Atta is the most specific information provided so far by the government on losses sustained by the security forces.
The militants, led by the jihadist Islamic State of Iraq and the Levant (ISIL), consolidated their control of the north of the country by capturing the Shiite-majority town of Tal Afar and its airport, a local official and witnesses said.
"The town of Tal Afar and the airport... are completely under the control of the militants," the official said on condition of anonymity. Witnesses said security forces had departed the town after days of heavy fighting, and confirmed that militants were in control.
Atta said that security forces were still fighting in the Tal Afar area, but added that, "Even if we withdrew from Tal Afar or any other area, this doesn't mean it is a defeat."
The town, which is located along a strategic corridor to Syria, had been the largest in the northern province of Nineveh not to fall to militants.
The latest advance came after insurgents at the weekend swept into the towns of Rawa and Ana in Anbar province, west of Baghdad, after taking the Al-Qaim border crossing with Syria.