The threat comes as the US and other nations have widened air strikes against Islamic State (IS) fighters in Iraq and Syria and a Syrian activist group has indicated that overnight strikes have hit three local oilfields near the Syrian IS stronghold of Raqqa.
Moreover, the London-based Syrian Observatory for Human Rights, have added that one civilian was killed in a strike on a plastics factory on the outskirts of Raqqa.
The Pentagon had earlier confirmed that jets had hit Raqqa as well as IS positions near the Turkish border.
The US-led coalition consisting of about 40 countries, including Arab states, has vowed to destroy IS, which controls large parts of north-eastern Syria and northern Iraq. Incidentally, the group's brutal tactics, including mass killings, beheadings, and abductions of members of religious and ethnic minorities, have triggered the international intervention.
Britain has become the latest country to join the coalition - two of six RAF Tornados based in Cyprus have carried out their first combat mission but returned without carrying out any strikes. Later, two RAF planes took part in a further flight and later returned safely. Probably they are testing the waters before embarking on offensive actions.
