NEW YORK — Syria escalated tensions with Turkey on Monday, accusing its neighbor and former friend of imperialist delusions harking back to the centuries of Ottoman dynastic rule, as Syrian Army gunners exchanged artillery blasts with their Turkish counterparts across the border for the sixth consecutive day.

Both insurgent sympathizers and the Syrian government described an extremely violent day in the nearly 19-month-old uprising in the country, with unverified accounts of killings and destruction in the embattled cities of Aleppo, Homs, Daraa, and in northern Idlib Province.