Supporters of President Jean-Bertrand Aristide came out in large numbers in capital Port-au-Prince to counter anti-Aristide protests on Thursday.
The United States closed its embassy and advised Americans against travelling to Haiti.
State Department spokesman Lou Fintor said the Haitian government had failed to maintain order in the capital and "in some instances has assisted in violently repressing the demonstrations".
"Some international organisations have decided to draw down their staff in Haiti," Finto said.
At least four people were shot at and injured, one of them in the head, witnesses said. It was not clear whether they were government supporters or opponents.
Aristide supporters also fired into the air and burned tyres in various Port-au-Prince neighbourhoods.
Government offices, international organisations, schools, petrol pumps and other businesses in the city downed shutters fearing violence.
On Thursday, thousands of students and others took to the streets to call for Aristide's resignation, blaming him for violence against protesters in the past. It was one of the largest political demonstrations in Haiti this year.
President Jean Aristide has been
blamed for earlier violence
On Friday morning, hundreds of Aristide supporters gathered in front of the National Palace and marched around the block, beating drums and singing.
Some chanted, "Cut off heads, burn down houses," a battle cry of the father of Haiti's independence, Jean-Jacques Dessalines, who led the country to independence from France in 1804.
Some demonstrators carried saws or swords and called out threats to students and journalists.
After Thursday's demonstration, Aristide supporters fired guns and threw rocks at the offices of two independent radio stations, Caraibes and Kiskaya. A third station, Radio Metropole, received threats and shut down its news service early.