"The interim government views today's events in Osh as an attempt by former President Bakiyev's associates to regain power," Farid Niyazov, a government spokesman, said.
The latest unrest is the biggest challenge to the interim government formed last month after a revolt against the five-year rule of Bakiyev, who fled to Belarus.
A Reuters witness in Kyrgyzstan's second-biggest city Osh said supporters of Bakiyev scuffled with guards and entered the government building after holding a demonstration that drew about 1,000 people.
The Kyrgyz government responded by saying it would take unspecified measures to restore authority in the area.
Al Jazeera's Robin Forestier-Walker, reporting from Almaty, said there is "certainly an air of real tension at the moment".
"This appears to be a co-ordinated action by those who are very unhappy about the fact that President Bakiyev was forced from power a little over a month ago," he said.
"The fact that it is co-ordinated tallies with what the interim government is saying that this is a 'coup attempt' and that they are going to do everything they can to put it down. But it remains to be seen how much support they have got, in terms of security, in order to quell such an uprising."
The interim government dispatched Ismail Isakov, the defence minister, to Osh to try to quell the revolt but it was not immediately clear what resources he had at his disposal.
There were conflicting reports about who controlled Osh airport. Reports said Bakiyev supporters had seized it but an employee at Osh airport said the airport had only been closed temporarily for Isakov's arrival and was now working normally.
Bakiyev fled Kyrgyzstan last month after an interim government seized power following street unrest that claimed 85 lives in the capital and elsewhere.
The interim government has since struggled to stamp its authority across the country, particularly in Bakiyev's southern power base.
On Wednesday, the interim government faced its first large public protest in the capital as hundreds of opponents - many members of Bakiyev's Ak Zhol party and the allied Communists - demonstrated against the dissolution of parliament.
The United States and Russia have both expressed support for the interim government, which has promised to hold new parliamentary elections in October. It was not immediately clear how they would respond to today's events.
"We are receiving information and are trying to understand what is happening", Dmitry Peskov, a spokesman for Vladimir Putin, the Russian prime minister, said.
|The interim government has struggled to stamp its authority across the country [AFP]
Both countries have air bases in Kyrgyzstan. The US base at Manas airport is key to Washington's efforts to supply forces fighting in nearby Afghanistan.
Bakiyev himself came to power in a 2005 revolt on the back of promises to build democracy and protect human rights.
He was backed at the time by Roza Otunbayeva who now heads the interim government.
Otunbayeva vowed to foil any coup attempt and promised to restore law and order, Interfax reported.
"We have what it takes to dispel the fear existing among the public," it quoted her as saying.
The south of Kyrgyzstan is Bakiyev's power base and Jalalabad is the former president's native region. The region is prone to ethnic tension between almost equally populous Kyrgyz and Uzbek communities.
Before the Soviet Union's collapse, hundreds of people were killed in clashes between Uzbeks and Kyrgyz near Osh in 1990.