EU foreign-policy chief Federica Mogherini has postponed a planned visit to Ukraine on March 30 after European Commission President Jean-Claude Juncker did the same.
President Petro Poroshenko's office said on March 28 that Juncker told Poroshenko he was postponing his visit "due to unforeseen health conditions."
Poroshenko's office said the visit would be held at a later date. Mogherini's visit was also called off.
Juncker and Mogherini had been expected to express support for Ukraine's pro-Western government, which is struggling with a Russian-backed rebellion in the east and severe economic troubles.
Former President Viktor Yanukovych's decision to spurn a major agreement with the EU in November 2013 led to protests that drove him from power.
Russia then seized Ukraine's Crimea region and lent support to separatists whose war with government forces has killed more than 6,000 people since April 2014.