Ukraine accuses Russia of sending tanks into territory

1. Ukraine has accused Russia of sending tanks into its territory.
2. Russia denies the accusations.
3. In Sept, Ukraine and pro-Russian rebels signed a ceasefire.
4. But tensions in southeastern Ukraine have increased recently.
5. On Sunday, rebels held elections fueling the conflict.
6. Russia faces pressure from West to reject the election results.
7. NATO is looking into the reports of tanks crossing the border.