Damascus, Nov 6 : Sounds of powerful explosions reverberated through a US base in Syria's northeastern province of al-Hasakah on Sunday night, a war monitor reported. The explosions were heard at the Qasrak base in the countryside of al-Hasakah followed by the presence of unmanned aerial vehicles hovering over the area, Xinhua news agency reported, citing the Syrian Observatory for Human Rights. The Observatory said uncertainty looms over the nature of the explosions, whether they were the consequence of routine military drills or deliberate targeting. The incident came a day after an explosion that rocked the vicinity of a US base in al-Shaddadi south of al-Hasakah, amid a surge in attacks against US military installations in eastern Syria by pro-Iran militias in response to US support for Israel in the ongoing conflict in Gaza, according to the Observatory. Over the past several days, these groups have executed a series of targeted assaults against US forces across various bases in northern and eastern Syria. According to the Observatory, a total of 15 attacks have been recorded since October 19, targeting several key US bases in Syria. /IANS