BAGHDAD - Iraq's military is drawing up plans to cope with any quick US military pullout, the defense minister said Monday, as a senior American official warned that the Bush administration may reconsider its support if Iraqi leaders don't make major reforms by fall.

The US official did not say what actions could be taken by the White House, but his comments reflected the administration's need to show results in Iraq -- as an answer to pressure by the Democrats in Congress seeking to set timetables on the US military presence.

Several mortar shells hit the US-controlled Green Zone, one striking the Iraqi parliament building but causing no casualties -- the latest in near daily barrages on the nerve center of the US mission and Iraqi government that underline the country's tenuous security.

At least 58 Iraqis were killed by attacks or found dead across Iraq, including seven people ambushed on a bus northeast of Baghdad, police said. The dead included 24 men whose bullet-riddled bodies were found across Baghdad, apparent victims of sectarian death squads.

British troops clashed with Shiite Muslim gunmen in the southern city of Basra. Britain's military said one British soldier and a civilian driver were killed when a supply convoy was attacked in the center of the city, Iraq's second biggest.

Elsewhere, US troops raided safe houses south of Baghdad but failed to find three soldiers missing since a May 12 ambush that left four other Americans and an Iraqi dead.

"We've (identified) some safe houses and we targeted a couple of those today and they were able to slip away from us. But we're going to come at things from a different angle," a US spokesman, Maj. Webster Wright, said without elaborating.

US officers said the search by thousands of US and Iraqi soldiers may be forcing the kidnappers to move the three Americans frequently, preventing insurgents from posting pictures of their captives on the Internet.

"We choose to be cautiously optimistic," Maj. Gen. Rick Lynch told CNN. "We're pursuing all leads with a passion, but right now we believe our soldiers are still alive. Each day that passes when we don't see proof of life, it causes us concern."

With violence raging, pressure is mounting on Prime Minister Nouri al-Maliki's government to demonstrate progress on key reforms or risk losing American support for the unpopular war.

On Monday, Defense Minister Abdul-Qader al-Obeidi told reporters Iraq's military was drawing up plans in case US-led forces left the country quickly.

"The army plans on the basis of a worst case scenario so as not to allow any security vacuum," al-Obeidi said. "There are meetings with political leaders on how we can deal with a sudden pullout."

It was unclear whether al-Obeidi's comment referred to routine contingency planning or reflected a feeling among Iraqi leaders that the days of US support may be numbered even though President Bush blocked an effort by Congress to set a withdrawal timetable.

A White House spokesman, Tony Fratto, said President Bush expressed confidence in al-Maliki during a telephone call Monday to the Iraqi leader.

He said the two talked about political progress in Iraq, and al-Maliki gave Bush updates on two key US demands -- legislation to share Iraq's oil wealth among its regions and ethnic groups and a reform of the constitution.

But two senior Iraqi officials told The Associated Press that Bush warned al-Maliki that Washington expected to see "tangible results quickly" on the oil bill and other legislation as the price for continued support.

The officials spoke on condition of anonymity because they weren't supposed to release the information.

In London, a senior US official echoed that warning, saying the Bush administration wanted signs of progress by fall or it would be forced to reconsider its policy in Iraq.

The official, who briefed reporters on condition his name not be published, said the top American diplomat and military commander in Iraq would submit a report on Iraqi progress in September.

"If one looks at when critical progress is to be made, one would be best advised to look at this fall as a key point," the official said.

Senior Kurdish lawmaker Mahmoud Othman confirmed that US pressure was mounting, especially on the oil bill, which was endorsed by the Iraqi Cabinet three months ago but has yet to come to the floor of parliament.

"The Americans are pressuring us to accept the oil law. Their pressure is very strong. They want to show Congress that they have done something so they want the law to be adopted this month. This interference is negative and will have consequences," Othman told AP.

Kurdish legislators oppose the formula for distributing oil revenues among the Iraqi communities, arguing for a greater say in how the money is disbursed.

Major Shiite and Kurdish parties oppose several proposed changes in the constitution, as well as Sunni Arab demands for a loosening of rules banning former Saddam Hussein supporters from government jobs.

Prospects for far-reaching agreements among Sunnis, Shiites and Kurds were thrown into doubt over the weekend when the leader of the largest Shiite party, Abdul-Aziz al-Hakim, was diagnosed with lung cancer at a hospital in Houston.

Al-Hakim, who left the US for treatment in Iran, delivered a televised address Monday in which he said he was suffering from a "limited tumor" but expected to return to the country soon.

US officials had been counting on al-Hakim to help push through reforms, and a lengthy absence could make it difficult to deliver Shiite support.

In other violence, the Iraqi newspaper Azzaman reported Monday that one of its reporters, Ali Khalil, 22, was kidnapped while leaving a relative's house in the increasingly volatile Baiyaa neighborhood of Baghdad and found dead several hours later. He is survived by his wife and week-old baby, the newspaper said.

The attack came three days after two Iraqi journalists working for ABC News were ambushed and killed on their way home from work. The New York-based Committee to Protect Journalists said 104 journalists -- not including Khalil -- had been killed in Iraq since the 2003 US-led invasion. About 80 percent of those were Iraqis, it said.

A roadside bomb exploded near a group of Iraqi soldiers patrolling the Sunni-dominated Adil neighborhood in western Baghdad, killing three and injuring two others.

In Muqdadiya, about 60 miles north of Baghdad, two gunmen killed two police officers as they walked by the police station.

Insurgents also fired mortar rounds into a bank in Baqouba while customers were lined up to collect their pensions, killing two people, police said.