A source in the Syrian Foreign Ministry said Sunday that Syria condemned the illegal visit made by the US Chairman of the Joint Chiefs of Staff, Mark Milley, to the country's northeast.

"Syria underlines that the illegal visit by the American Chairman of the Joint Chiefs of Staff is a flagrant violation of its sovereignty and territorial integrity," the source said.

Milley made the unannounced visit on Saturday to assess a nearly eight-year-old mission there and review safeguards for US troops against attack.

"The Syrian Foreign Ministry calls on the US administration to immediately stop its systematic and continuous violations of international law and its support for separatist armed militias," he added.

Damascus will not allow American acts to "derail it from combatting terrorism and safeguarding its sovereignty, security, and stability."

Milley told reporters in northeastern Syria that the "US forces and their partners in Syria, led by the Kurds, are making progress" against ISIS.

He also linked Washington's security with an alleged "mission" being carried out by the global coalition against Syria when asked if he believed that the operation in Syria was worth the risk.

Milley said "If you think that [US and allies' security] is important, then the answer is 'Yes,'" adding, "I think that an enduring defeat of ISIS and continuing to support our friends and allies in the region ... I think those are important tasks that can be done."

The US has for long employed the "ISIS threat", an alleged concern of Washington's, as a pretext to continue its illegal occupation of Syrian territories.

It has done so for two reasons: to destabilize the Syrian government and to pursue the systematic looting of the country's oil resources.

Even after the February 6 earthquake devastated several cities across the country, the US continues to loot oil from occupied Syrian territories. 

Syrian news agency SANA reported Saturday that US occupation troops have looted a new batch of oil from Syria's Al-Jazeera fields. 

The convoy was on its way to reach US military bases in Iraq via the illegal Al-Mahmudiya crossing in the Al-Yarubiya region.

According to civilian sources, the convoy is made of 23 vehicles and includes covered trucks and tanks filled with stolen oil.

The last time US troops plundered Syrian oil was on February 27th. The oil was looted from the same al-Jazeera fields and was transported to Iraq via illegal crossings. 

Mark Milley, ahead of his surprise trip, landed in occupied Palestine to discuss regional developments and further US Army-IOF cooperation.

During his visit, Milley was set to meet with Israeli Chief of Staff Herzi Halevi, and he planned to hold meetings with the Minister of Security and senior officials within the security establishment.

His visit to occupied Palestine came amid rising tensions within "Israel", with Israeli opposition leader Yair Lapid having previously warned that the passing of a controversial judicial reform law would cost "Tel Aviv" the United States and harm the economy, stressing that Washington was terrified of what is happening in "Israel".