The Armenian government declared a state of emergency after clashes between riot police and opposition protesters in the capital, Yerevan, left as many as eight people dead.

“The president declared emergency rule late last night and we have also stopped issuing accreditation for the foreign media,” a spokesman for the Armenian Foreign Ministry, Tigran Balayan, said by telephone yesterday from Yerevan.

Violence erupted yesterday in the capital, where anti-government demonstrators have held 11 days of rallies since the February 19 presidential election, in which former Prime Minister Serzh Sargsyan defeated Levon Ter-Petrosyan, a former president. The opposition claims that the vote was rigged.

America “deeply regrets” the unrest in Yerevan, and “calls on all sides to avoid further violence, act fully within the law, exercise maximum restraint, and resume political dialogue,” spokesman Sean McCormack said Saturday in comments posted on the State Department’s Web site. “We hope that the state of emergency declared today will be lifted promptly and that political dialogue resumes.”

Police used live ammunition and tear gas against the demonstrators, and Ter-Petrosyan was placed under house arrest, his spokesman, Arman Musinyan, said by telephone from Yerevan.

Mr. Ter-Petrosyan told reporters that he would continue his fight within the law and called for Western support, Mr. Musinyan said.

The election in the ex-Soviet state largely met Europe’s standards for democracy, though Mr. Sargsyan’s governing party denied media access to Mr. Petrosyan during the campaign and intimidated his supporters, according to election monitors of the Organization for Security and Cooperation in Europe.