BAGHDAD,(Reuters) – U.S. Ambassador Zalmay Khalilzad said some Iraqi leaders had miscalculated before thinking U.S. support would go on unconditionally but now they realise the patience of the American people is running out.

In an interview with CNN broadcast on Friday, Khalilzad echoed comments by Secretary of State Condoleezza Rice who said Prime Minister Nuri al-Maliki’s government was living “on borrowed time”. Khalilzad said Maliki realised diplomacy had not succeeded in dismantling militias and it was time for action.

U.S. President George W. Bush said he planned to send 21,500 more U.S. troops to Iraq as part of a new direction in Iraq that also involved putting more pressure on Iraqis to solve their political differences and take over their own security.

U.S. lawmakers in the Democrat-controlled Congress hammered Bush’s plan to send more troops, and many in Iraq questioned how much difference they can make. But Khalilzad said this time the Iraqi government was ready to take decisive action. “The president has been very resolute from the get go (from the start) and some people here have miscalculated perhaps, thinking no matter what they do or do not do support will go on because of the rock solid stand the president has taken,” Khalilzad told CNN. “The president has sent a very good strong message that the patience of the American people is running out,” he said.

Khalilzad said Maliki, a Shi’ite Islamist, had pledged his commitment to crack down on Shi’ite militias — a key demand of Washington and the Sunni Arab minority who blame the militias for operating death squads.

Washington has identified the Mehdi Army, a militia loyal to radical Shi’ite cleric Moqtada al-Sadr, as the greatest threat to security in Iraq. Maliki, who depends on Sadr’s political movement for support in parliament and government, has struggled to rein in the Mehdi Army, despite numerous pledges to allow nobody but the armed forces to carry weapons.

Asked if this time Maliki would really go after the Mehdi Army, Khalilzad said: “He has pledged this to the president of the United States, there will be no sanctuary. He has said to me that he has given diplomacy a chance with the militias, now we have to do whatever is necessary to get the job done.” “This is the best chance they have to move and if they don’t move they know that there’s a lot at risk for them as well.”

Maliki has promised a major new security plan for Baghdad that he said would crack down on armed groups regardless of sect or political affiliation. But with the sectarian loyalties of his police and army in question, success will be difficult.

Bombs, mortars and sectarian death squads have been killing hundreds of people every week and tens of thousands have fled their homes as the city, once a patchwork of mixed districts, has become more and more divided into sectarian enclaves.

Some of Bush’s fellow Republicans joined newly empowered Democrats in voicing scepticism that dispatching 21,500 extra troops to help regain control of Baghdad would work. More than 3,000 U.S. troops have died since the March 2003 invasion.

American peace activists held the first of what they said would be thousands of protests, vowing to take to the airwaves and the Internet in a campaign to block the plan, which they said had fuelled a fresh surge of anti-war sentiment.

A day after Bush vowed to disrupt what he called the “flow of support” from Iran and Syria for insurgent attacks on U.S. forces in Iraq, Iraqi President Jalal Talabani’s office said he would travel to Syria on Sunday for an official visit.

Democrats who want a phased withdrawal from Iraq to start in four to six months, lambasted Bush’s plan.

Senate Majority Leader Harry Reid said he expected to have the votes, with the support of some Republicans, to pass a resolution opposing the new deployment, which would bring American troop levels in Iraq to more than 150,000.

Though such a resolution is nonbinding and merely reflects opposition in the Senate. “I think that (bipartisan passage) will be the beginning of the end of the war in Iraq,” Reid said.