Gunmen in Baghdad ambushed a minibus as it drove through a Sunni neighbourhood bringing Shias from a funeral and killed 10 of those aboard, police said.
Elsewhere, a suicide bomber blew himself up outside the fortified Green Zone government compound, killing five people and wounding 10, as parliament prepared to meet a few hundred metres away.
The minibus attack in the violent southern Doura district comes a day after Iraq's prime minister pleaded for Iraqis to "unite as brothers" following a fresh spasm of violence over the weekend that pushed Iraq deeper into communal warfare.
Though bombings have claimed dozens of lives at a time, a wave of tit-for-killings between Shias and Sunnis in Baghdad has raised the spectre of all-out civil war, dealing a blow to Mr Nuri al-Maliki's hopes for national reconciliation.
Police said gunmen in cars opened fire on the minibus, which was returning from a funeral in the holy city of Najaf, 160 kilometres south of Baghdad.
Yesterday, gunmen ambushed a commuter bus in a Sunni district in western Baghdad and shot dead seven people. Earlier, two bombs in a Shia neighbourhood killed 12 and wounded dozens.
Addressing a heated session of parliament on a day, Ali al-Adib, from the Dawa party of Shia Prime Minister Nuri al-Maliki, said: "The country is sliding fast towards civil war."
The victims were returning from a funeral in the holy Shia city of Najaf when gunmen in two cars ambushed them. Maliki later condemned what he called "this awful crime" by terrorists "trying to incite sectarian strife".
A wave of tit-for-tat killings in Baghdad between majority Shias, oppressed under Saddam Hussein but now politically empowered, and the once dominant Sunni Arabs has deepened a centuries-old schism and raised the spectre of civil war.
In a rare sign of consensus among Iraq's divided leaders, the largest Sunni bloc said on Tuesday it would end a boycott of parliament after a call for unity by a Shia radical cleric and promises that a kidnapped legislator would be freed soon. Some Sunni leaders have blamed Shia militias loyal to Moqtada al-Sadr for the kidnapping of Taiseer al-Mashhadani, a charge they deny