Iraqi women, followers of radical Shiite cleric Muqtada al-Sadr, are seen on their way to attend Friday prayers in the Shiite stronghold of Sadr City in Baghdad. On Friday, al-Qaida in Iraq warned Shiites that “dark days soaked with blood” lie ahead and warned of a new campaign of attacks. Hours later a bomb went off outside a mosque south of Baghdad, wounding 20 people, police said. The banner in Arabic reads, “coming for martyrdom.”

Baghdad ? Many Iraqis are increasingly uneasy that a wave of bombings and shootings may revive all-out sectarian warfare that ravaged the country several years ago. In Baghdad and other cities, some are falling back into old cautionary habits — going outside only when necessary and avoiding busy markets and other crowded places.

These small but significant steps show the trepidation many Iraqis feel at a time when the country is floundering without a new government, facing threats of more attacks from al-Qaida-linked groups and making do with a dwindling number of U.S. troops.

“If this power vacuum and struggle continues, then everybody is expecting the worst. We are afraid that more attacks and more security deterioration will push the country in a new cycle” of violence, said Qassim Jassim, of Mahmoudiya, about 20 miles south of Baghdad. He said he and his family are staying home more often as a result.

On Friday, al-Qaida in Iraq warned Shiites in an announcement that “dark days soaked with blood” lie ahead with a new campaign of violence yet to come.

Hours later, a bomb went off outside a mosque south of Baghdad, wounding 20 people, police said. Ten people were also killed in the northern city of Tal Afar by a suicide bomber near a soccer field. Earlier this week, 119 people were killed across the country on Monday, and a botched car bombing killed nine people in Baghdad’s Sadr City on Wednesday.

Such attacks — many targeting Shiites — appear designed to provoke Shiite groups such as followers of anti-American cleric Muqtada al-Sadr to respond in kind.

Few people suggest the conditions right now are prime for a full-fledged sectarian war similar to 2006 — violence is still sporadic and nowhere near levels of just a few years ago; militias such as al-Sadr’s Mahdi Army, while throwing their weight around, haven’t taken up arms, and the neighborhood-against-neighborhood violence that marked the earlier fighting is absent.

Also, many say they are simply tired of the violence and will be even more wary this time before allowing their country to plunge into fighting.

But Iraqis are worried.

More than two months have passed since the March 7 election, in which none of the blocs won a majority in parliament. The resulting political stalemate has led to concern about ongoing attacks at a time when, many Iraqis charge, politicians are more focused on retaining their positions than on protecting the country.

In the election, a bloc led by Ayad Allawi, a Shiite with strong Sunni support, won the most parliament seats. Incumbent Prime Minister Nouri al-Maliki has challenged the results and has formed a coalition with fellow Shiites that potentially could exclude Sunnis.

“Sunnis will be very frustrated if (Allawi’s) list is sidelined in the new government,” said Omar al-Bayati, from Baghdad’s Sunni neighborhood of Azamiyah. “Many Sunnis think the formula of the current government should be changed; otherwise, the country is heading to the worst.”

Suspicion runs both ways. One of the victims of the Tal Afar bombings, Hussein Mizhir, said the mostly Shiite victims preferred to go to a Kurdish hospital in Dahuk, instead of the hospital in Mosul which is closer but is also a hotbed of Sunni insurgents.

Al-Qaida seems to determined to exploit any sectarian tensions. In its announcement on Friday, its umbrella group in Iraq also named a new so-called “minister of war” to replace its leader, Abu Ayyub al-Masri, who was killed in April.

At the time, U.S. and Iraqi officials touted the deaths of al-Masri and another high-ranking al-Qaida figure as a potentially devastating blow, but the Sunni terror group seems determined to show its relevance.

“It is clear that al-Qaida is trying to ignite the sectarian war in this country and with the latest attacks, I think that the civil war is a possibility,” said Alaa Mohammed, of the city of Hillah, about 60 miles south of Baghdad, scene of some of the worst bombings Monday.

Mohammed said he and his family are going shopping in the afternoon when markets are less crowded to protect themselves.

Many Iraqis are loath to say anything positive about the U.S. troop presence, but some worry about what will happen when American forces leave. The number of U.S. troops in the country is supposed to drop to about 50,000 by the end of August and all forces will leave by the end of 2011.

Iraqis on both sides of the sectarian divide have little trust in Iraqi security forces’ ability to protect the country. Many people are jaded by what they view as a system that values patronage over protection and frustrated at the ability of insurgents to carry out attacks despite Iraqi checkpoints at almost every turn.