London (CNN) -- At least 29 people were killed and dozens were wounded Thursday by a car bomb in Syria near the Turkish border, an opposition group said.
The blast took place at the Sajo bus station near the Bab al-Salama border crossing, the opposition Syrian Observatory for Human Rights said.
A civil war in Syria has left more than 100,000 people dead and millions displaced, according to the United Nations.
More than 100 civil society groups from around the world put their names Thursday to a statement urging the U.N. Security Council to back a resolution that would refer the situation in Syria to the International Criminal Court.
The statement, posted online by the New-York based Human Rights Watch, said it is time to end a culture of impunity that has seen atrocities committed by all sides.
"Neither Syrian authorities nor the leaders of non-state armed groups have taken any meaningful steps to ensure accountability for past and ongoing grave human rights crimes," it reads. "The failure to hold those responsible for these violations to account has only fueled further atrocities by all sides."
The groups said the ICC, as a permanent court set up to try war crimes, is the forum "most capable of effectively investigating and prosecuting" those responsible for the most serious crimes and for providing justice for the Syrian people.
The statement was issued as a core group of 11 foreign ministers from the so-called "Friends of Syria" met in London.
U.S. Secretary of State John Kerry and the head of the opposition Syrian National Coalition, Ahmad Jarba, were among those present for the talks, hosted by UK Foreign Secretary William Hague.
Asked about French Foreign Minister Laurent Fabius' assertion this week that France has seen indications the Syrian regime used chlorine gas some 14 times in recent months, Kerry said he had seen "raw data" suggesting there may have been "a number of instances in which chlorine has been used in the conduct of war."
That evidence is not confirmed, Kerry said, but if verified, it would be a violation of treaties Syria has signed. In that case, there would be "consequences," he said, although he would not specify what those might be.
Hague said those present had agreed to take further steps to increase support for the "moderate opposition" in Syria, including the National Coalition, and to boost the provision of humanitarian aid.
The foreign ministers also committed to doing "everything we can to hold the Assad regime accountable for the terror it is perpetrating, including through Security Council referral to the International Criminal Court," he said.
President Bashar al-Assad's government says it is combating terrorist groups.
Syrian Deputy Foreign Minister Faisal al Mekdad denied any use of chlorine gas by the government in an interview this week with CNN's Frederik Pleitgen in Damascus.
CNN's Shirley Henry and Elise Labott contributed to this report.