Vehicles have been banned from the streets of Baghdad for several hours, amid fears of bomb attack reprisals for the death of Abu Musab al-Zarqawi.
The death of the al-Qaeda in Iraq leader was announced on Thursday.
The vehicle ban coincides with Friday prayers and is in force both in the capital and in nearby Baquba, where Zarqawi was killed in a US air raid.
Thousands of worshippers go to mosques for Friday prayers and have often been targeted by bombers linked to Zarqawi.
Two car bombs exploded in mainly Shia areas of Baghdad on Thursday evening, killing 15 people.
"The curfew is a measure to keep people indoors as there could be more bombings like the ones last night, following Zarqawi's death," said an Iraqi defence ministry official.
The US military said the operation against Zarqawi had given them a "treasure trove" of new information.
The US struck after receiving specific tip-offs from within Zarqawi's organisation, officials said.
Iraqi Prime Minister Nouri Maliki said the $25m (£14m) bounty on Zarqawi's head would be honoured.
News of the militant's death has given a massive boost to the Iraqi government and the Bush administration, says the BBC's Middle East analyst Roger Hardy.
Shortly after the death was announced, the Iraqi parliament approved the key posts of defence and interior ministers, which had lain vacant despite the formation of a coalition government last month.
The new government has an ideal opportunity to persuade nationalist elements within the insurgency to join the political process, our correspondent says.
19 Aug 2003: Bombing of UN office in Baghdad, 23 dead
29 Aug 2003: Bombing of Najaf shrine killing Shia cleric Muhammad Baqr Hakim, 85 dead
2 March 2004: Co-ordinated attack on Shia mosques during Ashoura ceremony, 181 dead
11 May 2004: Nick Berg beheaded, first of at least nine foreign hostages killed in 2004
14 Sept 2004: Car bomb targeting police recruits in Baghdad, 47 dead
19 Dec 2004: Car bombs in Najaf and Karbala, 60 dead
9 Nov 2005: Triple attack on hotels in Amman, 60 dead
But, he says, it will have to perform better than its predecessors in its approach to divisive issues such as the constitution, corruption, the rising power of militias and failing basic services.
In an interview with Britain's Times newspaper, Mr Maliki promised "an initiative to secure Baghdad and confront the ethnic cleansing taking place... around the capital".
"We believe we will soon reach a tipping point in our battle against the terrorists as Iraqi security services increase in size and capacity," he said.
Zarqawi was known for his particularly gruesome tactics, including videotaped beheadings of hostages and synchronised bomb attacks on civilians.
Unrest has continued in Iraq with several attacks targeting workers and installations used by the oil industry:
- A senior official from Iraq's state oil company is kidnapped near his home in Baghdad
- Three oil engineers are reportedly shot dead on the road from Baiji to the oil production centre of Kirkuk
- Gunmen in Kirkuk attack an oil pipeline, reportedly killing one civilian and injuring three soldiers
On the streets of Baghdad, most people welcomed the news of Zarqawi's death.
"We consider this a great delight to the people because right must prevail," said one man. "Thanks are due to God for ending our ordeal."
But a statement on an Islamist website, purportedly from al-Qaeda, said: "The death of our leaders ... only makes us more determined to continue the jihad."
US Defence Secretary Donald Rumsfeld has dismissed as "utter nonsense" fears that Zarqawi's death will lead directly to more violence.
"These things tend to get planned well in advance," he said, after a Nato meeting in Brussels.
"You could have an upswing [in violence] but I think linking it to that would surprise me."
Jordanian intelligence reportedly assisted the US-led operation
Zarqawi traced to isolated safe house in the village of Hibhib approximately 10km outside Baquba, north-east of Baghdad
US aircraft launched air strike at about 1815 on Wednesday. Two F-16 aircraft dropped two 500lb bombs. The militant leader was reportedly holding a meeting with associates, including spiritual adviser Sheikh Abd-al-Rahman
Several others were reportedly killed
Iraqi police were first on the scene, followed by troops from the Multi-National Division North
Zarqawi identified by fingerprints, facial recognition and known scars