Islamic State militants have captured 16 Kurdish villages in northern Syria, Kurdish military officials said.
More than 100 Muslim leaders from across the UK have signed an open letter calling for the release of British aid worker Alan Henning.
The letter, printed in The Independent, is also supported by the Muslim Council of Britain which represents more than 500 Muslim organisations:
We, the undersigned British Muslim Imams, organisations and individuals, wish to express our horror and revulsion at the senseless murder of David Haines and the threat to the life of our fellow British citizen, Alan Henning ...
We plead with those holding Alan Henning to see the errors of their ways. To embrace the word of the Quran and accept that what they are now doing constitutes the worst condemnable sin.
A British aid worker who was with Alan Henning when he was captured by Islamic State militants in Syria has pleaded for mercy for his friend.
In an interview with BBC News, Majid Freeman had this message for Mr Henning's captors:
Please show him some mercy and understand he is a humanitarian aid worker. He's not a fighter, he's not come there for no political reasons, he's come there strictly to help the people. Please, please don't kill him.
He also spoke of Mr Henning's motivation in going to Syria:
When he seen the difference he made himself on the ground. When he went to the refugee camps, when he held a baby in his hands himself, it was very powerful for him. I think that changed his whole life.
The World Health Organisation and UNICEF have said they are providing a team of experts to help investigate how 15 children died following a vaccination programme in northern Syria.
A joint statement said that they supported the suspension of the programme "for as long as the facts remain unclear" but that it was vital to start it again as soon as possible.
A spokesman for the Syrian opposition's interim government has said that a muscle relaxant was wrongly used in vaccinations against measles.
The relaxant, which had similar packaging, was used instead of the dilute for the vaccine in the second round of vaccinations.
"The investigation is continuing to find out who is responsible," Mohammed Saad said.
Fifteen children have died after receiving vaccinations against measles in the northern Syrian province of Idlib.
The children, who died on Tuesday, were under two years old and dozens more were made sick. It was initially feared that as many as 40 children died.
The vaccination programme, which began in Idlib and Deir ez Zor on Monday, has been suspended while an investigation takes place.
Video footage of British hostage Alan Henning filmed the day before his capture in Syria has been released in which he describes his trips to the country as "worthwhile".
The 47 year old was kidnapped while travelling with a humanitarian aid convoy shortly after crossing into Syria from Turkey.
"It's all worthwhile when you see what is needed, as you get where it needs to go. That makes it all worthwhile," Mr Henning says in the video, filmed on Christmas Day 2013.
"No sacrifice we do is nothing compared to what they are going through every day," he adds.
American fighter, attack and remotely piloted aircraft conducted seven airstrikes against Islamic State of Iraq and the Levant terrorists in Iraq yesterday and today, US Central Command officials have reported.
One airstrike destroyed an ISIL armed vehicle northwest of the Haditha Dam, two airstrikes destroyed two ISIL armed vehicles northwest of Irbil.
Four airstrikes southwest of Baghdad destroyed several small ISIL ground units and a small boat on the Euphrates River that was resupplying ISIL forces in the area, officials said.
All aircraft exited the strike areas safely, they added.
Centcom has conducted a total of 174 airstrikes across Iraq, officials said.
US President Barack Obama would consider requests to "forward deploy" US military advisers with Iraqi troops "on a case-by-case basis" if they are needed, a White House spokesman has said.
They would not be personally or directly engaging the enemy
Iranian president Hassan Rouhani has issued a strongly-worded condemnation of Islamic State terrorists he says are trying to "kill humanity".
In an interview with NBC News, Mr Rouhani said IS murders of civilians were contrary to Islamic teachings.
"From the viewpoint of the Islamic tenets and culture, killing an innocent people equals the killing of the whole humanity," Mr Rouhani said.