Damascus, Dec 22 : Pro-Iran militias have launched 60 attacks on American bases in Syria since October 19 in retaliation for the US' backing of Israel during the Gaza conflict, a war monitor reported. The attacks, which included rocket shells and drone strikes, have been targetting the US bases in eastern Syria rather than the energy fields that some US bases were built on, said the Syrian Observatory for Human Rights on Thursday. The Britain-based watchdog group said the attacks had recently escalated as the Israeli military campaign in the Gaza Strip continued, noting that the US forces are tight-lipped about their losses, Xinhua news agency reported. In previous reports, the observatory noted that these attacks were launched from inside the Iraqi territories and targeted US bases in the eastern province of Deir al-Zour near the Iraqi border. /IANS