At least 155 people died in Syria Thursday on another deadly day in a crisis that started 18 months ago. Here's a look at key developments:

Violence rages in and around Damascus

Regime forces and their allies killed at least 21 people in the Damascus suburb of Moadamieh Thursday, an opposition group said. They are among 68 people killed in Syria's capital and its countryside, the opposition Local Coordination Committees of Syria said. At least 87 others were slain elsewhere in Syria, the group said. State-run TV described a government operation in the northern Aleppo province that killed and injured "a number of terrorists."

Envisioning Syria after al-Assad

Italy plans to host an international meeting soon to explore the world's "role and responsibilities" in Syria if and when President Bashar al-Assad leaves office, the foreign minister said Thursday. In a column for the Italian daily La Repubblica, Giulio Terzi said the talks in Rome will touch on "security, institution building, economic reconstruction and humanitarian" initiatives.

Western and Arab nations have been trying to hasten political change and end the war in Syria for months. Terzi said the European Union, which includes Italy, must play a "front-line role" in transition efforts. The foreign minister spoke of a "sense of urgency" in the international community to end the war.

U.S. and Turkish officials, meanwhile, talked about the Syrian situation in Ankara, the Turkish capital, the Turkish Foreign Ministry said.

Britain, echoing U.S., warns of military intervention if Syria uses chemical weapons

Britain and the United States would "revisit their approach" to Syria if the Syrian government uses chemical weapons, the British prime minister's office said.

Prime Minister David Cameron and President Barack Obama spoke by phone late Wednesday and agreed that the use of chemical weapons would be "completely unacceptable," the office said.

Obama said this week that the Syrian government would risk crossing a "red line" and invite U.S. military intervention if it uses chemical weapons.

The Syrian Foreign Ministry said last month that Syria has chemical and biological weapons but would use them only against foreign attackers.

U.S., Britain and France urge more aid

The United States, Britain and France want more countries to heed a U.N. warning about the humanitarian situation.

Obama told Cameron in a phone call about "his concerns about the increasing dire humanitarian situation in Syria, and the need for more countries to contribute" to United Nations appeals, the White House said.

Cameron and French President Francois Hollande described the growing number of refugees as a concern, Cameron's office said.

Rights group condemns both sides

Amnesty International accused both sides of committing war crimes during the battle for Aleppo, Syria's largest city.

The group said it investigated about 30 attacks that killed 80 people who were not involved in fighting.

Amnesty blamed the regime for targeting civilians. Some attacks were indiscriminate and others appear to have been direct attacks on civilians or civilian objects.

The opposition, namely members of the rebel Free Syrian Army, bound and executed members of a state-armed militia group, Amnesty said.

Al-Assad's government has denied killing civilians. The rebel army has vowed to investigate the killings.