Adding to the tension, Iran launched missiles at Islamic State targets in eastern Syria on Sunday, a strike seen as a projection of military power into part of Syria identified as a top priority by Damascus and its allies.
A statement released by US Central Command on Sunday said the Syrian jet was "immediately shot down.in accordance with rules of engagement and in collective self-defence of Coalition partnered forces".
U.S. support of anti-Islamic State militias such as the ones in At Tanf and the Syrian Democratic Forces has increasingly put it into direct conflict with Syria and its allies Russia, Iran, and Shiite militias.
It was observed heading toward coalition forces, who were outside the outpost, officials said. "Their course was on a run toward our folks to drop a munitions on them".
The downing of the regime jet led Moscow to say it would sever a vital hotline it uses to communicate with the United States coalition to avoid mishaps in Syria's increasingly crowded and complicated battle-space.
On Monday, Russia's defense ministry effectively drew a line across Syria west of the Euphrates River, saying that "all kinds of airborne vehicles, including aircraft and UAVs of the global coalition. will be tracked by the Russian SAM systems as air targets".
"Air operations continue and de-confliction measures are ongoing", a United Kingdom government spokesperson said Tuesday.More news: US shoots down pro-regime drone in Syria
More news: Republican Handel wins Georgia House election
More news: Lawyer says Trump not under investigation, despite president's tweet otherwise
With the skies over Syria growing increasingly crowded, a statement from the Australian Defence Department released in the capital, Canberra, said that "Australian Defence Force protection is regularly reviewed in response to a range of potential threats". "We call on Russian Federation to continue to use these measures".
Australia has deployed about 780 military personnel as part of the US-led coalition fighting so-called Islamic State (IS) in both Iraq and Syria. Until now, says the BBC's Jonathan Marcus, "the co-ordination mechanism has generally worked well and its operation is as much in Moscow's as Washington's interest".
Russian Federation on Monday suspended a crucial safe flights over Syria deal with the US under a memorandum after it shot down a Syrian regime's fighter jet on Sunday.
"This is not the time for the coalition to be in disarray", Dr Lina Khatib, head of the Middle East and North Africa Programme at Chatham House, an global affairs think tank, told CNN.
The chairman of the Joint Chiefs of Staff said the United States was working to restore the "deconfliction" communications line with Russian Federation.
Gayle Tzemach Lemmon, a senior fellow at the Council on Foreign Relations, said Monday that the downing of the Syrian jet, together with Iran firing missiles into Syria over the weekend, marked "a dramatic escalation in a war the United States had not meant to fight".
The US military said that it will continue to shoot down "pro-regime aircraft" if they persist to pose a threat to coalition and allied militias.
The line was established in October 2015 after Russian Federation entered Syria's civil war to prop up President Bashar al-Assad.