The sudden successes of the militant forces sent hundreds of thousands of people running, some literally, from the new outbursts of violence, panicked leaders in Turkey and Syria and revived memories of bloody American struggles to wrest the same places — Mosul and Tikrit — from jihadist fighters a decade ago.
By late Wednesday, the Sunni militants, many aligned with the radical Islamic State of Iraq and Syria, were battling loyalist forces at the northern entrance to the city of Samarra, about 70 miles north of Baghdad. The city is known for a sacred Shiite shrine that was bombed in 2006, during the height of the American-led occupation, touching off a sectarian civil war between the Sunni minority and Shiite majority.
Militant commanders were reportedly threatening to destroy the shrine if its defenders refused to lay down their arms, while hundreds of Shiite fighters were said to be heading north from Baghdad to confront the attackers.
As Iraqi government forces crumbled in disarray before the assault, there was speculation that they may have been ordered by their superiors to give up without a fight. One local commander in Salahuddin Province, where Tikrit is located, said in an interview Wednesday: “We received phone calls from high-ranking commanders asking us to give up. I questioned them on this, and they said, ‘This is an order.’ ”
Residents of Tikrit reported remarkable displays of soldiers handing over their weapons and uniforms peacefully to militants who ordinarily would have been expected to kill government soldiers on the spot.
Mr. Maliki, a Shiite, himself suggested the possibility of a disloyal military in his exhortations on Tuesday for citizens to take up arms against the Sunni insurgents.
As the central government declared a 10 p.m. curfew in the capital and surrounding towns, an influential Iraqi Shiite cleric, Moktada al-Sadr, called for the formation of a special force to defend religious sites in Iraq. The authorities in neighboring Iran, which is predominantly Shiite, canceled all visas and flights for pilgrims to Baghdad and intensified security on the Iran-Iraq border, Iran’s official Islamic Republic News Agency reported.
Shiite militia leaders said that at least four brigades, each with 2,500 to 3,000 fighters, had been hastily assembled and equipped in recent weeks by the Shiite political parties to protect Baghdad and the political process in Iraq. They identified the outfits as the Kataibe Brigade, the Assaib Brigade, the Imam al-Sadr Brigade and the armed wing of the Badr Organization.
Perhaps the greatest danger is that the Iraqi conflict could draw in neighboring countries. particularly Turkey, a NATO ally. On Wednesday, insurgents were holding scores of Turkish citizens seized in Mosul over the last two days, including the Turkish consul general, other diplomats and at least three children, the Turkish government said.
Prime Minister Recep Tayyip Erdogan of Turkey was holding an emergency meeting with top security officials, and the Turkish foreign minister, Ahmet Davutoglu, cut short a trip to New York and was returning to Ankara. “No one should try to test the limits of Turkey’s strength,” Mr. Davutoglu said in a statement.
Turkey has long taken an interest in northern Iraq for economic reasons and because of the sizable and often restive Kurdish minority, which straddles the border and controls a region of Iraq east of Mosul.
Iraq’s foreign minister, Hoshyar Zebari, was quoted on Wednesday as saying his country’s Kurdish minority would “work together” with Baghdad’s forces to “flush out these foreign fighters.”
At a meeting of Arab and European foreign ministers in Athens, Mr. Zebari, a Kurd, called the insurgents’ strike “a serious, mortal threat,” adding: “The response has to be soon. There has to be a quick response to what has happened.”
Iraqi Kurds are concentrated in the autonomous region of Kurdistan, where security is maintained by a disciplined and fiercely loyal fighting force, the pesh merga, that has not yet become involved in the clashes.
