Iraqi Prime Minister Haidar al-Abadi arrived in Tehran late Monday on his first visit to Iran since taking office after the crisis triggered by the advance of Islamic State militants.
Iraqi state television said Abadi, whose country remains beset by IS, arrived shortly before midnight for talks with Iranian officials including President Hassan Rouhani about the ongoing battle, which has drawn in US and other international air strikes.
IS fighters hold towns just a few miles (kilometres) from the Iranian border, and the Islamic republic has been reported by senior Kurdish officials to have deployed troops inside Iraq.
Abadi's visit is all the more important given his surprise elevation to the premiership after the removal in August of Nuri al-Maliki, the Iraqi prime minister whom Iran had resolutely backed since 2006 until this summer's cataclysmic events.
Maliki's armed forces failed in the face of a lightning surge by IS fighters into Iraq from Syria, eventually resulting in him stepping down from the top job after Iran publicly endorsed Abadi's candidature as premier.
No schedule has been released but Abadi's trip is expected to last one day only. Iran has supported the Baghdad government throughout the crisis and was the first country to send arms to Kurds fighting IS militants in northern Iraq.
Major General Qassem Suleimani, the chief of Iran's elite Quds Force, has been spotted in Iraq, where it is believed he played a key role in coordinating military operations.
As Shiite neighbours, Iran and Iraq have been close since the removal of Sunni dictator Saddam Hussein in the US-led invasion of 2003.
Speaking earlier in the city of Najaf after a rare meeting with the most revered figure among Iraqi Shiites, Grand Ayatollah Ali al-Sistani, Abadi ruled out any foreign ground intervention to assist government forces in retaking territory lost to jihadists and urged Sunnis to give up such hopes.
"No ground forces from any superpower, international coalition or regional power will fight here," Abadi told reporters, reiterating previous remarks on the issue.
"This is my decision, it is the decision of the Iraqi government."
Some officials and Sunni tribal leaders in areas most affected by the unrest have argued the world should step up its involvement from air strikes to a ground intervention against IS.
Iraqi state television said it was the first time in four years that Sistani had met a high-ranking Iraqi government official.
Abadi's talks in Iran on Iraq's war against IS come with the situation in the balance. Since June, the militants have seized control of swathes of Iraq and brought it to the brink of collapse.