In this photograph posted on the internet, a man holds up his hand covered in blood during clashes between demonstrators and riot police in Tehran, Iran

Iran's capital, Tehran, was tense Sunday, following a week of sometimes violent opposition protests against a disputed election victory by incumbent President Mahmoud Ahmedinejad June 12.

On Saturday, thousands of protesters took to the streets and clashed with police, despite a warning by the country's supreme leader to halt demonstrations. State-run television reported 13 people were killed.

Witnesses in Tehran said riot police used tear gas, batons and water cannons to disperse supporters of defeated presidential candidate Mir Hossein Mousavi.

Parliament Speaker Ali Larijani, meanwhile, told an interviewer on Iranian TV (according to Iran's Press TV) that the opinion of those who think the results from the disputed presidential election are not accurate, should be respected. Iran's Press TV quoted him as saying it was necessary to abide by the law and urging "politicians and candidates" to pursue their claims through legal channels, saying the issue should not be taken to the streets.

Supporters of opposition leader Mir Hossien Mousavi set fire to a barricade as they hurl stones during a protest in Tehran

He called on the powerful body that supervises elections, the Guardian Council, to use every possible means to convince protesters that their complaints will be thoroughly investigated.

In a speech to parliament, Larijani also criticized the United States, Britian, France and Germany, saying they were interfering in Iran's affairs.

On Saturday, U.S. President Barack Obama urged Iran's government to "stop all violent and unjust actions against its own people."

In his strongest response to Iran's post-election unrest, Mr. Obama said the Iranian government must understand that the world is watching. He called on Iran to "govern through consent, not coercion."

Analysts say a power struggle continues between Iran's veteran former President Ali Akbar Hashemi Rafsanjani and Iran's Supreme Leader Ayatollah Ali Khamenei, despite Khamenei's praise for Mr. Rafsanjani during Friday's prayers in Tehran.