Police in Iraq say a train carrying oil tanks has exploded, killing at least one person and injuring several others.
Witnesses reported massive clouds of smoke above the railway line
The blast was said to have been caused by a bomb, but it was not yet clear if the train was the intended target.
Meanwhile, the US military has said two soldiers were killed and one hurt by a bomb near Baghdad on Wednesday. Several Iraqi troops died in attacks elsewhere.
Iraq's Foreign Minister Hoshyar Zebari has also condemned the killing of two Algerian diplomats abducted last week.
A group claiming to be al-Qaeda in Iraq posted an internet statement on Wednesday saying it had killed Algerian envoys Ali Balarousi and colleague Azzedi.
Mr Zebari complained that "neighbouring countries" were doing too little to stop foreign fighters crossing their borders into Iraq.
Speaking at a news conference with new US ambassador Zalmay Khalilzad, he said: "Iraq's security is part of the security of these countries."
The blast on a seven-tanker convoy carrying oil occurred in the Doura neighbourhood of southern Baghdad, police said.
Witnesses reported a huge fire and a massive cloud of smoke over the railway line, but were unsure whether the train or a nearby police checkpoint was the intended target.
Six Iraqi soldiers have been killed in clashes with insurgents in two towns north of Baghdad on Thursday, the Reuters news agency has reported.
Security sources said fighters had fired mortars and guns at checkpoints in Baquba and Khan Bani.