Russian President Vladimir Putin said on Thursday that the presence of U.S. troops in Syria was "illegitimate," following Washington's decision to withdraw its troops from the war-torn country.

During his annual press conference that was attended by some 1,700 journalists, Putin said Americans should not have entered Syria in the first place, adding that Russia was invited by the Syrian government to fight terrorism in the country.

Putin said he was skeptical whether the United States would pull all its troops out of Syria. Moscow had not noted any sign of a U.S. withdrawal, he indicated.

Citing the example of Afghanistan, Putin said the U.S. has said many times it was leaving the country, but still retains a military presence there.

"But it's possible (that U.S. troops will withdraw from Syria)," he said, calling it the "right decision."

U.S. President Donald Trump said on Wednesday that the U.S. had defeated the radical ISIL group in Syria, and that this fulfilled the only goal for keeping U.S. troops in the country.

"Donald is right and I agree with him," Putin said, noting that he largely agreed with Trump that ISIL has been defeated.

Commenting on the issue, Chinese Foreign Ministry spokeswoman Hua Chunying said on Thursday that Beijing always respects Syria's sovereignty and territorial integrity, stressing that the future of Syria should be decided by the Syrian people.

"We hope all sides involved can make joint efforts to create conditions for an early start of a Syrian-led inclusive process, and work towards the resolution of the Syria issue at an early date," she added. "This is in line with common interests of all parties in the international community."

At the press conference, Putin also expressed his hope that the work to form a constitutional committee for Syria is reaching final phases. He accused UN Special Envoy for Syria Staffan de Mistura of delaying the creation of the committee.

On Tuesday, the foreign ministers of Russia, Iran and Turkey said they have agreed to make efforts at convening the first session of the Syrian Constitutional Committee in early 2019.

Russia is doing everything to bring the over seven-year Syrian conflict toward a political resolution, Putin told the reporters.

'Russia-China ties facilitate world stability'

Putin praised enhanced trade relations and joint achievements made by China and Russia in the past year.

"Russia and China reached 100 billion U.S. dollars in trade this year, it is a benchmark," Putin said, adding that the two countries will not stop and pursue further economic cooperation.

Meanwhile, Putin noted Russia and China are not only working on economic collaboration, but are also cooperating on international issues, saying their close correlation will facilitate world stability.

He also hailed China's development under the reform and opening-up program as Beijing celebrates the 40th anniversary of the landmark policy this year.

Russia wants to 'normalize' ties with U.S., Japan

Putin warned about the dangers and threats of underestimating a nuclear war, stressing that lowering the threshold for the use of nuclear weapons could lead to global catastrophe. 

The Russian president said he hopes that common sense would prevail on this important issue.

Speaking about U.S.'s withdrawal from the Intermediate-Range Nuclear Forces (INF) treaty, he said it's hard to predict the consequences and that Russia will respond by creating a new type of weapon.

Putin said to the audience that Moscow must normalize relations with Washington, adding that Russia will do so when the U.S. is ready. But Putin admitted he does not know whether he will meet with Trump.

Ties between Moscow and Washington have further worsened in the past year over Russia's alleged meddling in U.S. elections, the poisoning of Russian ex-spy Sergei Skripal in Britain, and the Russia-Ukraine standoff in the Black Sea.

Trump canceled a planned bilateral meeting with Putin on the sidelines of the recent Group of 20 (G20) summit in Argentina.

Meanwhile, the Russian leader said he wanted to normalize relations with Japan, despite concerns over Tokyo's motives to deploy a U.S. air defense system in the country.

"And I have said many times and I can repeat it again: We do not consider these to be defensive weapons," he said. "It's part of American strategic nuclear potential placed on the periphery."

Russia and Japan have been in disputes for several decades over island territories captured by Soviet troops during the final days of World War II.

"We aim and will sincerely aim at reaching a peace treaty with Japan," he stressed.

Spy case aimed at 'holding Russia back'

Putin dismissed the case of Skripal's poisoning as aimed at undermining Russia's international standing.

Britain has blamed Russia for the scandal, but Moscow has strongly denied any involvement.

"There is only one aim: to hold back Russia's development as a possible competitor," the Russian president said.

He added that sanctions on Russia imposed by Western countries were the result of Moscow's increasing international influence. 

"This is connected with the growth of Russia's power," he said. "A powerful player appears who needs to be reckoned with. Until recently it was thought there was no longer such a country."

Sanctions are "just a reason to constrain Russia's progress," Putin stressed, noting that the Russian economy has "adapted to these external constraints." 

Putin, 66, was re-elected as Russia's president in March. His fourth term will end in 2024.