The United States and the European Union on Monday urged Syria to “end violence immediately” and allow a peaceful and democratic transition of government.

A joint statement, issued after the annual summit of U.S. and European leaders in Washington, also called on Damascus to allow human rights observers and foreign journalists into the country.

A United Nations commission investigating allegations of human rights violations in Syria issued a similar call Monday, telling the Syrian government to “put an immediate end to the violence, investigate rights violations and bring the perpetrators to justice.”

A report issued by the commission said the Syrian military has committed crimes against humanity in its brutal crackdown on anti-government protesters. It accused Syrian troops of “summary execution, arbitrary arrest, enforced disappearance, torture, including sexual violence, as well as violations of children's rights.”

The report will now go to the Human Rights Council and the U.N. General Assembly, which will decide what to do next.

The European Union said it planned to impose additional sanctions on the embattled government of Syrian President Bashar al-Assad. EU foreign ministers will vote Thursday to further restrict trade and economic dealings with Damascus. The EU and the United States already have sanctions in place against Syria.

Tens of thousands of Syrians protested against unprecedented economic sanctions imposed by the Arab League Sunday. Syrian Foreign Minister Walid Muallem said they amount to “a declaration of economic war against Syria.”

Arab officials proposed the sanctions after Syria refused to accept a Friday deadline they set to allow league observers into the country to monitor the government's response to the eight-month uprising.

Rights groups say Syrian forces killed at least 23 people across the country on Sunday.

The United Nations says more than 3,500 people have been killed since March in connection with the uprising.