ZOLOCHIV, Ukraine, Sept 13 (Reuters) - Ukraine's President Volodymyr Zelenskiy called on the West to speed up deliveries of weapons systems as Ukrainian troops move to consolidate control over a large swath of northeastern territory seized back from Russia.

Since Moscow abandoned its main bastion in northeastern Ukraine on Saturday, marking its worst defeat since the early days of the war, Ukrainian troops have recaptured dozens of towns in a stunning shift in battleground momentum.

A senior U.S. military official said Russia has largely ceded territory near Kharkiv in the northeast and pulled many of its troops back over the border.

Washington and its allies have provided Ukraine with billions of dollars in weapons that Kyiv says have helped limit Russian gains. In a video address late on Monday, Zelenskiy said Ukraine and the West must "strengthen cooperation to defeat Russian terror".

U.S. Secretary of State Antony Blinken said Ukrainian forces have made "significant progress" with Western support.

"What they have done is very methodically planned out and of course it's benefited from significant support from the United States and many other countries in terms of making sure that Ukraine has in its hands the equipment it needs to prosecute this counteroffensive," Blinken said during a news conference in Mexico City.

Washington announced its latest weapons programme for Ukraine last week, including ammunition for HIMARS anti-rocket systems, and has previously sent Ukraine NASAMS surface-to-air missile systems, which are capable of shooting down aircraft.

Zelenskiy said Ukraine had recaptured roughly 6,000 square km (2,400 square miles) of territory, a sliver of Ukraine's overall land mass of around 600,000 square km. The recaptured land is approximately equivalent to the combined area of the West Bank and Gaza.

Russia has taken control of around a fifth of Ukraine since its troops invaded on Feb. 24.