Iraqi state television announced that a four-hour traffic ban in force every Friday to curb bomb attacks on mosques during weekly prayers would be extended through most of the day.
The regular Friday ban on traffic in Baghdad from 11am to 3pm has been extended to 7pm for the day, state media said. An overnight curfew operates from 9pm to 6am
A gun and grenade attack on a market just outside Baghdad on Monday and a suicide car bombing to the south of the capital killed 120 people this week.
US data showed that attacks on security forces in Baghdad have risen to 34 a day this week, up from 24 a day in recent months.
Baghdad morgue alone has taken in 1,000 bodies this month.
American commanders are speaking about a fight to the finish in the capital between the unity government of Nuri al-Maliki, the Shia prime minister, and Sunni Arabs with links to Saddam Hussein, the former president.
Describing the capital as a "must-win" for the rebels and the government, a US military spokesman said on Thursday that al-Maliki's month-old security clampdown in Baghdad had achieved only a "slight downtick" in violence, with civilian deaths steady.
"They will do an all-out assault against the Baghdad area," Major-General William Caldwell said. "We have seen the movement of terrorist elements into the Baghdad area. We have seen the flow occurring."
American forces have also been going after some Shia leaders, many of them apparently rogue elements of pro-government militias that al-Maliki has promised to rein in.
British forces in the Shia southern city of Basra said they arrested two men in separate operations early on Friday.
"We strongly suspect them of terrorist activities ... including executions, kidnappings, attacks on Coalition forces bases and patrols and attacks on Basra civilians," Major Charlie Burbridge, a British military spokesman, said.