Iran and Syria condemned a US plan to help rebels fighting to topple president Bashar Assad, and signalled that he intends to stay in power at least until the 2014 presidential election.
The remarks came against the backdrop of a strategic victory for the regime as the military regained control over a string of villages along a key highway to open a potential supply route in Syria's heavily contested north.
The army command boasted of the achievement in a statement, saying it had eradicated the remnants of "terrorist agents and mercenaries" in the area that links the government-controlled central city of Hama with Aleppo's international airport.
The reversal of gains, confirmed by Syrian activists, has the potential to change the outcome of the battle in Aleppo, Syria's largest city where government troops and rebels have been locked in a stalemate for months.
Syrian rebels have long complained that they are hampered by the world's failure to provide heavier arms to help them battle Assad's better-equipped military. The international community is reluctant to send weapons partly because of fears they may fall into the hands of extremists who have been gaining influence among the rebels.
But US secretary of state John Kerry announced on Thursday that the Obama administration was giving an additional £40 million in assistance to Syria's political opposition and would, for the first time, provide non-lethal aid directly to the rebels.
In an interview timed to coincide with Mr Kerry's first foreign trip as the top US diplomat, Assad told the Sunday Times that "the intelligence, communication and financial assistance being provided is very lethal".
In their first official statements on the US decision, the Syrian and Iranian foreign ministers accused Washington of having double standards and warned it would only delay an end to the civil war.
Syrian foreign minister Walid al-Moallem and his Iranian counterpart, Ali Akbar Salehi, also set clear parameters for any future talks with the opposition, saying that whether Assad stayed or went would be decided in the presidential election scheduled for next year. And Mr Salehi went further to say Assad may run for another term.
"Assad is Syria's legal president until the next elections. Individuals have the freedom to run as candidates. Until that time, Assad is Syria's president," Mr Salehi said at a joint news conference in Tehran.