In the city of Petit-Goave, about 70 kilometres (45 miles) west of the capital Port-au-Prince, more than 1,000 people demonstrated against Mr Aristide - his supporters pelted them with rocks.
In Gonaives, some 130 km north of the capital, anti-government protesters clashed with 200 heavily-armed members of a street gang known as the Cannibal Army which is said to be loyal to the president.
At least nine people have been injured this week, including a high school student who is in critical condition after being shot twice in the head.
Over the last two weeks, there have been a number of opposition protests and violent counter-demonstrations by armed supporters of the president which have paralysed city streets and businesses.
"The situation is very delicate and we fear civil war," Prime Minister Yvon Neptune said on Monday.
Opposition groups are calling for the removal of Mr Aristide, a former Roman Catholic priest now in his second term as president.
Haiti
Aristide re-elected in 2000 in a poll boycotted by the opposition
First elected president in 1990 - ousted by a coup seven months later
Returned to power in 1994 with US backing
Business leaders accused the authorities earlier this week of allowing what they called a "climate of terror" to dominate the country.
Haiti is one of the poorest countries in the region and correspondents say the worsening economic situation has contributed to discontentment with Mr Aristide.
The government has accused the private sector of pushing for "foreign intervention".
Officials blame much of the nation's insecurity on a lack of support from international financial institutions.
The international community suspended millions of dollars in aid to Haiti after the disputed May 2000 elections, which gave Mr Aristide's governing Lavalas Family party most of the parliamentary seats.