Two rockets struck a base housing American troops in eastern Syria on Wednesday without causing any human or material losses, the US military said.  The morning attack on Mission Support Site Conoco came as Iran and its allies in the region marked the third anniversary of the killing of Iran’s leading general and chief of the Quds force, Qassem Soleimani, in a US drone strike in the Iraqi capital, Baghdad.  No one claimed responsibility for the attack in eastern Syria, where it is not uncommon for bases housing US troops to come under rocket fire or mortar attacks. Iran-backed militia are based nearby as are sleeper cells of the ISIS group that was defeated in Syria in March 2019.  The Britain-based Syrian Observatory for Human Rights, an opposition war monitor, said the rockets were fired by Arab tribesmen in the region who are armed by Iran.  “Attacks of this kind place Coalition Forces and the civilian populace at risk and undermine the hard-earned stability and security of Syria and the region,” said Joe Buccino, spokesman for the US Central Command, in a statement.  CENTCOM said members of the Kurdish-led and US-backed Syrian Democratic Forces (SDF) visited the site from which the rockets originated, and found a third that was not fired.  The SDF announced later Wednesday that they arrested a senior figure in the ISIS group, the militants financial official from Deir Ezzor province. His arrest comes amid a dayslong campaign by the US-backed force against ISIS sleeper cells in parts of northeastern Syria that have claimed responsibility for deadly attacks in recent weeks.  There are roughly 900 US troops in Syria, including in the north and farther south and east.