John McCain
Sen. John McCain (R-AZ) leaves a meeting where a new version of a GOP healthcare bill was unveiled to Republican senators at the Capitol, Washington, DC. July 13, 2017. Getty Images

President Donald Trump's decision this week to end the CIA's program to arm moderate Syrian rebels —indicating his inclination for developing a constructive working relationship with Russia — hasn't gone down well with Arizona Sen. John McCain.

Just a day after being diagnosed with brain tumour, Mc Cain plunged into the political scene Thursday by condemning the president's move to halt the program, which was training the rebels to fight Bashar al-Assad's regime.

McCain, an ardent critic of Trump's policies in Syria, said in a statement if the reports were true, the Trump administration was clearly "playing right into the hands of Vladimir Putin."

"Making any concession to Russia, absent a broader strategy for Syria, is irresponsible and short-sighted. The administration has yet to articulate its vision for Syria beyond the defeat of ISIL, let alone a comprehensive approach to the Middle East," he said.

The Arizona senator also tweeted his disapproval of Trump's decision Thursday.

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Trump's officials said the decision to scrap the program was made nearly a month ago after an Oval Office meeting with CIA Director Mike Pompeo and National Security Adviser H.R. McMaster. This meeting was held ahead of the July 7 meeting with Russian President Vladimir Putin at the G20 Summit in Germany, according to the Washington Post.

After Trump's meeting with Putin, the two countries agreed to support a new cease-fire in southwest Syria, along the Jordanian border, where units of Syrian rebels backed by CIA have been operating for many years.

Not just Syria, McCain also blamed Trump for not formulating a strategy for the Middle East.

"There is still no new strategy for victory in Afghanistan either. It is now mid-July, when the administration promised to deliver that strategy to Congress, and we are still waiting," he added.

Last month, Trump gave Defense Secretary Jim Mattis authority to send more troops to Afghanistan to train Afghan forces to push back the gains made by the Taliban, the Islamic State group (ISIS) and other militant groups, the New York Times reported, citing officials.

Read: US Army Private Killed In Afghanistan, 7 Other Military Fatalities In 2017

However, critics say the U.S. has still not created an effective strategy for Afghanistan, where it is involved in the longest war in America's history.

Last month, McCain criticized the military strategy in Afghanistan, less than two weeks after three U.S. soldiers were killed in a Taliban attack, reports said. Citing an Afghan soldier who had turned his gun against Americans, McCain said it was time to "turn the situation around in Afghanistan." He also expressed his concern that even after 16 years of war, the U.S. was at a stalemate in Afghanistan, and the most worrisome aspect was that Washington had no strategy to end that stalemate and achieve victory.