"As the fires in France and Spain continue to ravage, European solidarity knows no limit," von der Leyen wrote on X on Wednesday.
She said Romania and Greece had extended their support missions to the fire-hit regions, while Poland would join the operation on Saturday.
"Thank you for your courage and commitment," she wrote.
Polish Deputy Prime Minister and Defence Minister Władysław Kosiniak-Kamysz announced earlier this week that Poland would assist Spain's firefighting efforts by deploying firefighters and equipment aboard military CASA transport aircraft.
France and Spain have activated the European Union Civil Protection Mechanism, under which member states have deployed 13 firefighting aircraft, four helicopters, 134 firefighters and 41 fire engines, Polish state news agency PAP reported.
Seven aircraft and four helicopters have been sent to France, while six aircraft have been deployed to Spain, it said.
According to the European Forest Fire Information System (EFFIS), about 300,000 hectares of land have burned in France and Spain so far this year.
France's interior ministry said more than 13,500 wildfires have burned through 116,000 hectares since January, the largest area on record.
Spain's Ministry for the Ecological Transition said 153,000 hectares burned during the first half of the year, six times the area affected during the same period last year.
(gs)
Source: PAP