Russia has pulled back thousands of its troops from the Ukraine border after multiple demands by Western powers, followed by sanctions by the U.S. and the European Union, U.S. defense officials said late on Thursday.

However, according to the officials, nearly seven battalions and a few thousand troops still remained on the border, which was earlier estimated to have as many as 40,000 Russian troops. The removal of the troops took place after multiple announcements by Russian President Vladimir Putin that he had ordered such a withdrawal, Wall Street Journal reported.

“They are not where they need to be and won't be until all of their troops that they positioned along that border a couple of months ago are gone,” Defense Secretary Chuck Hagel told media while traveling to Singapore. “We do know that thousands of Russian troops have been pulled back and are moving away. But we also know that there are still thousands of Russian troops still there that have not yet moved.”

On Thursday, Obama administration officials, including Hagel, expressed concerns about the increasing violence in the restive eastern Ukraine, including Thursday’s attack on a military helicopter, which was shot down by pro-Russian rebels, killing 14 people, after days of a violent stand-off between pro-Russian rebels and Ukrainian army forces in the Donetsk region.

Both the White House and the U.S. State Department said it is time Russia pressured the separatists to end the crisis and free a group of international monitors who were detained in eastern Ukraine earlier this week, Associated Press, or AP, reported.

“We are disturbed by the ongoing violence in eastern Ukraine,” Jay Carney, a White House spokesman, was quoted by AP as saying. “We are concerned that this indicates separatists continue to have access to advanced weaponry and other assistance from the outside.”