The EU foreign affairs chief was speaking on Monday, less than 24 hours after another six Ukrainian soldiers were killed in the Donbass region, the latest to lose their lives in the long-running bloody conflict with Russian-backed separatists.
Mogherini also praised the reform process in Ukraine which, with the war in the country's east showing no sign of ending, was taking place "in extremely difficult conditions."
The Italian-born official's comments came during a news conference in Brussels with Stepan Kubiv, the first deputy Prime Minister of Ukraine.
Earlier, the two officials signed a number of agreements, further demonstrating, said Mogherini, the EU's "ongoing commitment to Ukraine and to the ongoing reform efforts that Ukraine is undertaking."
Mogherini said that in light of the deaths in Donbass at the weekend it was important to reaffirm the EU's support for Ukraine's independence, sovereignty and territorial integrity.
She said both the EU and Ukraine agreed at Monday's Association Council meeting that "complete" implementation of the Minsk arrangements by all sides was "crucial."
The duration of sanctions against Moscow was linked to this, Mogherini said.
She also condemned the "severe deterioration" of human rights in Crimea and its "militarisation" by Russia.
The Association Council meeting was held one month after the successful 18th EU-Ukraine summit, and a week after the EU released a joint report examining the state of play of Ukraine's implementation of its association agreement since 1 January 2015
Mogherini the agreement was "already producing results", including a "significant" 44 per cent increase in trade between the EU and Ukraine.
Her comments were largely echoed by Kubiv, who met with Mogherini in place of Ukraine's Prime Minister, Volodykmyr Groysman, who was forced to remain in Kyiv to deal with a banking crisis.
Speaking alongside Mogherini, he described the deceased Ukraine soldiers as "heroes" and said they had sacrificed their lives in the continuing fight towards the development of democracy in Ukraine.
He said the agreement supporting Ukraine's public administration reform is worth €104m, and is one component of a larger package totalling €300m of EU support for accountable and transparent governance in Ukraine.
In addition, a series of cross-border cooperation agreements were signed. These programmes, he said, will promote continued economic and social development in regions on both sides of common borders and addressing common challenges in a range of priority areas, as well as to ensure efficient and secure borders.
Later on Monday, the European Investment Bank (EIB) and Ukraine were due to sign the latest set of loans, totalling approximately €600m and underpinned partly by EU grants, in the total €3bn financial assistance programme for 2014-2016.
This is part of the €11bn EU support package announced by the EU in March 2014, and, according to Mogherini, demonstrates the EU's commitment to helping Ukraine "stabilise its economic and financial situation, increase resilience, and act as a catalyst for prosperity for the citizens of Ukraine."