Iraq's deputy prime minister said Saturday his country still needs the U.S. military to ensure security and warned that time is running out to approve a new security deal with Washington.

West of Baghdad, a suicide bomber killed eight people and wounded 17 more at a police checkpoint near the former Sunni insurgent stronghold of Ramadi in Anbar province, police said.

The bomber stepped out of his car at the checkpoint and blew up his explosive vest, said police Col. Yassin Duweich. Seconds later the car exploded, apparently detonated remotely by an accomplice nearby.

Three more people died in roadside bomb attacks in Baghdad and in Madian, south of the capital.

The attacks come as U.S. and Iraqis officials have been working to finalize a deal that would remove U.S. troops from Iraq's cities by June 30 and withdraw them from the country by 2012.

Deputy Prime Minister Barham Saleh cautioned that Iraq will enter a "period of a legal vacuum" if the U.N. mandate under which US troops operate in Iraq expires by year's end without the agreement having been approved.

Without a deal or new U.N. mandate, the U.S. would have to cease all operations in the country.

On Thursday, Washington delivered what it calls its final answer to proposed Iraqi changes to the draft agreement, and is now waiting on Baghdad's move.

Saleh said the government was studying the latest amendments, and expressed hope the deal will be resolved "as soon as soon possible because time is running out." He added the pact is key to preserving "the security improvement which has been achieved" in recent months.

Also Saturday, Iraq's prime minister called for changes to the Iraqi constitution to give more power to the central government, especially in security and other key fields.

The comments by Prime Minister Nouri al-Maliki, who was a member of the committee that drafted the constitution in 2005, appeared directed at the Kurds, who enjoy extensive autonomy in their three-province region of northern Iraq.

But it may also have been directed at his Shiite rivals who want a similar, nine-province autonomous region in the south.

"A strong federal government must be built which has full responsibility over security, sovereignty and other issues," al-Maliki said in Baghdad.

His remarks came against the backdrop of rising tension in the north between Kurds and Arabs, who have accused the Kurds of trying to expand their region to include areas under central government control.

The Kurds have also signed contracts with foreign oil companies to exploit oil fields in their region. The Oil Ministry maintains those contracts are illegal. The constitution gives the Kurds the right to maintain their own military force — the peshmerga — that is responsible for security in the Kurdish region.

Al-Maliki said the current constitution was written "in haste," when Iraq was in a "transitional stage," and that the time has come to revise it.

"Since we managed to establish the government and to protect it from collapsing and from terrorism, killers and the followers of the former regime, today we should move forward in building it on clear national and constitutional bases in which responsibilities are specified," he said.

He said a possible solution would be to give regional governments say over their economic, agricultural, investment and local administration matters, while leaving security and foreign affairs to Baghdad.

Kurdish politicians promptly dismissed al-Maliki's proposals, defending their regional rule.

"We reject any attempts to limit the powers of the Kurdistan region or any other province," said Falah Mustafa Bakir, in charge of foreign relations in the Kurdish regional government.

Another prominent Kurdish lawmaker, Mahmoud Othman, said while central government should be strong enough, "this does not mean that the government should be the controller of everything while regions and provinces have no power to do anything."

But al-Maliki suggested that the failure to tackle these issues would leave open the door to future violence.

"We have a conflict over one inch here and over a line there," he said. "If there is no clear vision of the political system and sovereignty, we will turn into real governments fighting each other."

Al-Maliki's main coalition partner — the Supreme Islamic Iraqi Council — wants to create a similar self-ruled region in the nine-province Shiite south. Al-Maliki's Dawa Party, which is also Shiite, and the movement of radical Shiite cleric Muqtada al-Sadr, oppose the autonomous region as a threat to national unity.

The issue is expected to take prominence in the provincial elections set for January. The Supreme Council needs to take control of provincial governments to push through its autonomy plan.