The president declared a four-day state of emergency in Mongolia's capital early Wednesday after protesters stormed the headquarters of the ruling party, alleging fraud in weekend parliamentary elections.

President Nambaryn Enkhbayar's decree allowed police to use force in dealing with the thousands of rock-throwing protesters who thronged the headquarters of the Mongolian People's Revolutionary Party and set it on fire. The crowd had not dispersed despite repeated volleys of tear gas, rubber bullets and water cannons.

"Police will use necessary force to crack down on criminals who are looting private and government property," said Munkhorgil, the minister of justice and home affairs, who like some Mongolians goes by one name. Ulan Bator was also placed under a 10 p.m. to 8 a.m. curfew, he said.

The crowd thinned slightly after the emergency declaration, though some protesters had begun looting paintings from an art gallery and televisions from government offices. Others vandalized parked cars.

Enkhbayar, a ruling party member, acknowledged the protesters' complaints over results of the election—centered on how to share the country's mineral wealth—but appealed for calm.

"Let's sit down and solve the election fraud," he said on national TV.

Mongolia, a mostly poor nation sandwiched between China and Russia, is struggling to modernize its nomadic, agriculture-based economy. According to the government, the per capita income is just $1,500 a year in the country of about 3 million people spread across an area the size of Alaska.

The two main political parties focused their campaigns on how to tap recently discovered mineral deposits—including copper, gold and coal—but disagreed over whether the government or private sector should hold a majority stake.

The difference meant the outgoing parliament was unable to pass an amendment to the Minerals Law, which kept the government from concluding investment agreements with international mining giants to develop mineral deposits in the Gobi Desert.

The existing law gives the government the right to take up to a 50 percent interest in an important mineral deposit if state funds were used to discover it.

The proposed change would give Mongolia a minimum 51 percent stake. But while the ruling party wants the government to hold that stake, the Mongolian Democratic Party says private Mongolian companies should be able to hold it.

Tuesday's clashes far surpass the usual minor violence that has often accompanied elections in the 18 years since Mongolia cast off communist rule for democracy. Police seemed unprepared to deal with the crowd, who trampled one police officer, apparently leaving him badly injured.

Police spokesman Sainbayar said 26 police officers were hospitalized and one was blinded. An additional 30 or 40 people were also taken to hospitals with various injuries, he said. A Japanese journalist was seriously injured with a head wound.

Complaints of election fraud originally centered on two districts in Ulan Bator that were awarded to the ruling party, but contested by two popular members of the Civic Movement party. Following that, protesters called the entire election into question, with opposition Democrats saying that their party, not the MPRP, won the poll.

Some protesters pushed into the General Election Commission offices to demand that officials resign over voting irregularities and fraud. The commission defended the vote, but at least one party called for a recount in some districts of Ulan Bator.

"The Mongolian people voted for democracy and not for the MPRP, who are ex-communists," said Magnai Otgonjargal, vice chairman of the Civic Movement party.

According to preliminary results, the MPRP—which also governed the country when it was a Soviet satellite—won 46 seats in Sunday's vote. That would give the party far more than half of the 76 seats in parliament, called the State Great Khural.

The other major party, the Mongolian Democratic Party, took 26 seats. An independent won one seat and a minor party another. Results in two other seats were not yet clear. The election commission has until July 10 to announce the final results.