The U.S. Central Command chief huddled Monday with Iraq's prime minister in the third unexpected visit by a top U.S. official in recent days, signaling a possible prelude to shifts in American policy on engaging Iran and Syria. Raging sectarian violence killed scores more — 20 of them in a bus bombing.

Gen. John Abizaid, commander of all U.S. forces in the Middle East, also sternly warned Nouri al-Maliki that he must disband Shiite militias and give the United States proof that they were disarmed, according to senior Iraqi government officials with knowledge of the what the two men discussed.

Beyond that, Abizaid asked the Iraqi leader to give the U.S. military a firm timetable for when Iraq's security forces could take full control of the country, the officials said on condition of anonymity because of the sensitive nature of the talks.

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A brief government statement said Abizaid told al-Maliki he had come to "reaffirm President Bush's commitment" to success in Iraq. It also said the two discussed the "effect of neighboring countries on the security situation in Iraq," a clear reference to Iran and Syria.

That was particularly significant given that al-Maliki had said only a day earlier that he was ready to take "five steps" toward Syria if it took one in Iraq's direction.

After more than two decades of virtual estrangement between Damascus and Baghdad, the al-Maliki government has invited Syrian Foreign Minister Walid Moallem to visit and he accepted, although no date had been set.

What's more, the American blue-ribbon bipartisan commission trying to devise a new course for the war in Iraq, which met with President Bush and other White House officials Monday, was widely expected to recommend that the administration engage Iraq's neighbors in a bid to tamp down the raging violence.

The Iraq Study Group plans to announce its recommendations to Bush and Congress by the end of the year.

The reference to Iraq's neighbors coincided as well with a call by British Prime Minister Tony Blair for Iran and Syria to help stem bloodshed in Iraq and to join efforts to deliver stability across the Middle East.

In a major foreign policy speech Monday night, Blair warned there would be no incentives or concessions for doing so and that any failure to assist would lead to international isolation for the two countries.

Blair was to speak with the Iraq Study Group by video-link Tuesday. Britain has been the Bush administration's key ally in the Iraq war and still has about 7,000 forces mainly in the south of the country.

The Syrian ambassador to Washington affirmed a readiness to work with the United States.

"We in Syria believe that engagement with the United States on Iraq can help a lot, because we believe that we need to stabilise the situation in Iraq and support the political process there," Imad Moustapha told the British Broadcasting Corp.

Both Washington and Baghdad charge Syria with doing to little to close its border with Iraq to foreign fighters, especially Al Qaeda operatives. Beyond that top members of Saddam Hussein's former regime have found safe haven in Syria, where they have operated freely in helping fund and organize the Sunni insurgency that is responsible for the vast majority of U.S. deaths in Iraq.

As for Iran, many of key figures in Iraq's now-dominant Shiite hierarchy spent years in exile there during Saddam's rule. One Shiite militia was trained by Iran's elite Revolutionary Guard. Iran is known to fund that militia and one loyal to radical Shiite cleric Muqtada al-Sadr. Both are believed deeply involved in the sectarian killing that is tipping Iraq toward all-out civil war.

Abizaid was the third top U.S. official to visit Iraq since Oct. 30, and the meeting comes a day after al-Maliki promised to shake up his government in a bid to end the sectarian slaughter. National Security Adviser Stephen Hadley's was first to visit, followed five days later by U.S. National Intelligence Director John Negroponte.

The intelligence chief also demanded that al-Maliki disband militias by year's end, but was met with a flat rejection. Al-Maliki told Negroponte such a move would be political suicide. Al-Maliki, a Shiite, relies heavily on two major Shiite political groups which run the heavily armed militias.

In Monday's session with Abizaid, the government said, the CENTCOM chief "emphasized the multi-national forces commitment to training Iraqi security forces to handle security in all Iraqi provinces."

Al-Maliki has been pressing the United States to move more quickly to hand security affairs over to his army, claiming it could crush violence in the country within six months.

The top U.S. commander in Iraq, Gen. George Casey, recently said it would take 12 to 18 months before Iraqi security forces were ready to control the whole country with some U.S. backup.

Abizaid apparently called al-Maliki's bluff during the Monday meeting by asking the prime minister to give a detailed explanation about how he would do that. The Iraqi government officials said Abizaid asked for "proof that Iraqi security forces were capable of controlling the security situation in order for us to give you more powers as the commander in chief."

Such a move seemed distant Monday as at least 85 more Iraqis died violently, and the U.S. military reported the deaths of four more soldiers. The American deaths raised to 2,852 the number of U.S. forces who have died since the U.S. invasion in March 2003. So far this month, 34 American service members have been killed or died in Iraq.

The bomb that killed 20 was planted on a bus in the northeast Baghdad Shaab neighborhood and detonated shortly after noon at a major intersection, police said. Sunni insurgents have frequently targeted Shiite bus passengers in the ongoing sectarian reprisal killings that are tearing at the fabric of Iraqi society.

Hours earlier, Mohammed al-Ban, a cameraman for Iraq's independent Al-Sharqiyah satellite television broadcaster, was gunned down leaving his home in the northern city of Mosul. His wife was wounded, police said.

Al-Ban is the second journalist for the channel to be killed in recent weeks. Anchorwoman Leqaa Abdul Razzaq was fatally shot late last month as she was traveling in south Baghdad's lawless Dora district.

At least 89 journalists have been killed in Iraq since hostilities began in March 2003, according to an Associated Press count based on statistics kept by the New York-based Committee to Protect Journalists. Another 35 media employees, including drivers, interpreters and guards, have been killed, all but one of them Iraqi.

Gunmen mowed down at least 24 other people, including a city councilman and a Sunni sheik, in executions and assassinations around Iraq. Elsewhere at least 46 bodies were found shot and with signs of torture.