  We present the results of the $UBVI_C$ variability survey in the young open
cluster NGC 6611 based on observations obtained during 34 nights spanning one
year. In total, we found 95 variable stars. Most of these stars are classified
as periodic and irregular pre-main sequence (PMS) stars. The analysis of the
$JHK_S$ 2MASS photometry and four-colour IRAC photometry revealed 165 Class II
young stellar sources, 20 of which are irregular variables and one is an
eclipsing binary. These classifications, complemented by $JHK$ UKIDSS
photometry and $riH\alpha$ VPHAS photometry, were used to identify 24
candidates for classical T Tauri stars and 30 weak-lined T Tauri stars. In
addition to the PMS variables, we discovered eight $\delta$ Scuti candidates.
None of these were previously known. Furthermore, we detected 17 eclipsing
binaries where two were previously known. Based on the proper motions provided
by the Gaia EDR3 catalogue, we calculated the cluster membership probabilities
for 91 variable stars. For 61 variables, a probability higher than 80% was
determined, which makes them cluster members. Only 25 variables with a
probability less than 20% were regarded to be non-members.
