Syria’s rebels have made no bones about their opposition to the upcoming Syrian election, and met today’s election rally in the southern city of Deraa with mortar fire, killing at least 39 people, many civilians, and wounding over 200 others.

The US-armed Free Syrian Army (FSA) claimed credit for the attack, saying they considered campaign rallies a “very provocative” move and had warned civilians not to take part.

As the election campaign picks up across the government-held parts of Syria, rebels seem likely to try to disrupt such events, but the large number of civilian deaths sparked criticism from UN Secretary-General Ban Ki-moon.

The US has not addressed today’s attack, but has repeatedly hyped its increased weapons provision to the FSA as “carefully vetted” rebels. It is unclear if the mortar bomb used in today’s attack was provided by the US, or one of the other nations backing the rebels.