Reports say a large structure has been installed in Pyongyang's Kim Il-sung Square, raising speculations that North Korea could be preparing for a possible visit by Russian President Vladimir Putin.

According to Voice of America(VOA) on Wednesday citing satellite photos taken the day before by U.S. satellite service Planet Labs, a "large object" that had never existed before was spotted in the square.

North Korea has previously installed structures in Kim Il-sung Square and mobilized personnel for preparations when high-ranking officials from China or Russia have visited, or when military parades have been held.

VOA added that there was no movement spotted at Pyongyang's Mirim airfield, where activity is observed during military parades.

Meanwhile, North Korea's state-run Korean Central News Agency(KCNA) reported on Tuesday that regime leader Kim Jong-un had sent a congratulatory message to President Putin on the occasion of Russia Day on Wednesday, mentioning the meaningful bond and close comradely relationship between the two countries.