BAGHDAD >> Vice President Joe Biden arrived in Iraq early Thursday for talks about the future of American troops in the country as they prepare to leave at year’s end, but three explosions in the capital killing two people demonstrated the lingering security challenges facing the country.

Biden’s unannounced trip marks the first visit by a top U.S. official since Iraq approved a new Cabinet last month, breaking a political deadlock and jump-starting its stalled government after March’s inconclusive elections.

“I’m here to help the Iraqis celebrate the progress they’ve made. They’ve formed a government and that’s a good thing. Biden told reporters before meeting with Ambassador to Iraq James F. Jeffrey and Gen. Lloyd Austin at the U.S. Embassy in Baghdad.

“They have got a long way to go,” he acknowledged.

Iraqi officials said they expected the issue of whether to keep some U.S. forces in Iraq beyond the Dec. 31 deadline would dominate Biden’s talks Thursday with President Jalal Talabani, Prime Minister Nouri al-Maliki and Kurdish President Massoud Barzani.

The officials spoke on condition of anonymity to be able to discuss the sensitive diplomatic issues frankly.

Under a security agreement between Washington and Baghdad, all American troops are to leave Iraq by the end of the year. However, Iraq’s top military commander has said U.S. troops should stay until Iraq’s security forces can defend its borders — which he said could take until 2020.

But al-Maliki, under pressure from hardline Shiite Muslims, has signaled he wants American troops to leave on schedule. Last weekend, the influential and anti-American cleric Muqtada al-Sadr returned to Iraq after nearly four years of exile, in part to insist that the U.S. “occupiers” must leave on time or face retribution among his followers “by all the means of resistance.”

Al-Sadr, who headed one of Iraq’s Shiite militias blamed for deadly attacks on U.S. troops, met Wednesday with Grand Ayatollah Ali al-Sistani in Najaf, one of Iraq’s holiest Shiite cities, in a step to gain credibility among the nation’s clerics and in its political circles. Aides to both men refused to discuss details of their evening meeting.

Both Washington and Baghdad refused to discuss publicly any possibility of U.S. troops staying until after Iraq installed its new government.

Moreover, the Obama administration has maintained it would leave on time unless Iraq’s officials asked the U.S. to reconsider the security agreement and allow at least some troops to stay.

Just under 50,000 U.S. forces remain in Iraq, and American military leaders have said privately they will need to already start planning by early spring on how to get them home unless told otherwise.

Keeping troops in Iraq presents a political headache for both President Barack Obama, who is up for re-election next year and promised to end the war in his 2008 campaign, and for al-Maliki, who held onto a second term as prime minister only with al-Sadr’s support.

The visit is Biden’s seventh since January 2009. He arrived in Iraq after stops in Afghanistan and Pakistan, where the U.S. has refocused its efforts against al-Qaida and allied extremist groups that threaten American security.

Biden was last in Baghdad in September for a military ceremony at the end of U.S. combat operations in Iraq. His son, Beau, returned to the U.S. in 2009 from a yearlong deployment in Iraq with an Army National Guard unit.

Iraqi police officials said three mosques — two Sunni and one Shiite — were targeted by the roadside blasts Thursday morning. Eleven people were also wounded. The blasts were outside the fortified Green Zone that houses the U.S. Embassy and Iraqi government offices where Biden’s meetings were likely to take place.

The officials spoke on condition of anonymity because they were not authorized to speak to the media.