US Vice President Dick Cheney, on a surprise trip to Baghdad on Monday, strongly urged Arab states like Saudi Arabia to open full diplomatic ties with Iraq if they want to counter Iranian influence.
A series of bomb blasts greeted Cheney's high-security and secrecy-shrouded arrival, while later in the day a suicide attack near the Shiite shrine city of Karbala killed at least 41 people, officials said.
The attacks underscored the deadly violence that still grips the nation five years after US bombs began dropping on Baghdad to topple Saddam Hussein.
"Our Arab friends would do well to send ambassadors to Iraq," Cheney told a news conference in Baghdad.
"If Arab states (are) concerned about Iranian influence in Iraq, one of the ways for them to counter that is to make a commitment to have a presence here as well."
US officials have expressed frustration that regional heavyweights Saudi Arabia and Egypt have not yet formally appointed and sent ambassadors to Baghdad.
Cheney was to push Saudi King Abdullah on the issue later this week.
A visit to Baghdad by Iran's hardline President Mahmoud Ahmadinejad two weeks ago was seen as a sign of Tehran's rising sway over Iraq's Shiite-led government at a time when Iraq is fighting to curb Shiite-Sunni sectarian strife that has killed tens of thousands of people.
On a trip marking the fifth anniversary of the war, Cheney criss-crossed the strife-torn capital to assure Iraqi leaders in their homes or offices of "unwavering" US support as they "consolidate and strengthen their democracy".
But much of Cheney's visit focused on securing fragile security gains and completing the unfinished business of encouraging Iraqis to pass legislation seen as key to defusing sectarian violence and fostering national reconciliation.
Cheney said he saw "phenomenal" and "dramatic" security improvements since his last visit, in May 2007, mid-way through a surge in US troop numbers that saw an additional 30,000 personnel deployed to Iraq.
"I'm pleased to be able to return next week to Washington and report to the president that we are making significant progress in Iraq," said Cheney, who called the surge "a real success story".
"If you look back on those five years it has been a difficult, challenging but nonetheless successful endeavour," said Cheney. "It has been well worth the effort."
Cheney held talks with the top US commander in Iraq, General David Petraeus, and US ambassador Ryan Crocker, who are due to make a progress report to the US Congress on April 8-9 that is expected to shape debate on the drawdown of the 158,000 or so US troops.
US Republican presidential hopeful John McCain was also in Baghdad on Monday to assess the success of the "surge" strategy of which he has been a big supporter, his aides said.
His Democrat rivals hope the vastly unpopular war will help them hold the US Congress and recapture the White House in November's elections.
The conflict has claimed the lives of nearly 4,000 US troops as well as tens of thousands of Iraqi civilians and -- by the Pentagon's conservative estimate -- cost upwards of 400 billion US dollars.
Another two US soldiers were killed on Monday when a roadside bomb struck their vehicle north of Baghdad, the military said.
But in a bid to highlight the improved situation in Baghdad, Cheney left the fortified Green Zone, which houses most government offices and the US embassy, to meet President Jalal Talabani, his two deputies and leading Shiite politician Abdel Aziz al-Hakim.
The US vice president travelled in a 11-vehicle convoy guarded by heavily armoured Humvees and Apache helicopters for his foray on to the capital's streets.
After his meeting with Cheney, Hakim said his views were "identical" with the US vice president, helping to "guide work on the long-term strategic relationship" with Washington that is currently under discussion.
The two governments are negotiating a new basis for the presence of US troops beyond this December when the UN mandate under which they currentlty operate expires.
Cheney's visit to Iraq was the first stop on a nine-day Middle East tour which will also take him to Oman, Saudi Arabia, Israel and the West Bank, and Turkey.
He was to stay overnight at a military base away from Baghdad and then address US troops on Tuesday.