In Ulan Bator, the Mongolian capital, five people have died and more than 300 were hurt in violent protests over alleged electoral fraud, says Tsend Munkhorgil, the Justice minister.
He said that hundreds of people were reportedly detained.
A state of emergency and curfew has been declared by the president, and parts of the city have been sealed off.
Early results from Sunday’s poll give a clear victory to the ruling party, and have been questioned by opposition supporters.
Preliminary returns suggest that at least 45 seats in the 76-seat parliament have been taken by the ruling Mongolian People’s Revolutionary Party (MPRP), but the opposition Democrats allege fraud.
After these results emerged on Tuesday, several thousand people gathered on to the streets of the capital. The ruling party headquarters were set alight and government offices were looted. At the national art gallery, paintings were destroyed by a fire, said Mongolia’s Montsame news agency.
Tear gas, rubber bullets and water cannon have been used by the police, in order to force stone-throwing protesters back.
‘Use necessary force’
Though Justice minister Munkhorgil said five people had died, he gave no further details of those killed.
He said that a Japanese citizen, thought to work for a news organisation, was among the injured.
A four-day state of emergency has been announced late on Tuesday by president Nambaryn Enkhbayar, to run from 23h30, local time.
“Police will use necessary force to crack down on criminals who are looting private and government property”, said Mr Munkhorgil.
The capital has been placed under a 2200 to 0800 curfew, and alcohol sales have reportedly been banned.
By Wednesday morning, an Associated Press reporter in Ulan Bator said that though some roadblocks remained in place, shops were open and transport was running.
Montsame said that later in the day, lawmakers and officials will meet in the capital for emergency talks on the situation.
The polls were free and fair, said the MPRP as well as international observers.
But Tsakhia Elbegdorj, Democratic Party leader, said his party was robbed of victory.
“If most people voted for us why did we lose? We lost because… corrupt people changed the results”, he said.
Since 1990, when Mongolia adopted wide-ranging economic and politics reforms, this is the fifth election in the country. Before that, its government was modelled on that of the neighbouring Soviet Union.
From 1921 to 1996, the MPRP ruled Mongolia, before being beaten by the Democrats. In 2004 the two parties were forced into an uneasy coalition from which they broke apart two years ago.
The two parties disagree on how newly-found mineral reserves – copper, gold and coal – should best be exploited.