diff --git a/rules/tel.js b/rules/tel.js
index aa57ea3..d7698e9 100644
--- a/rules/tel.js
+++ b/rules/tel.js
@@ -5,9 +5,24 @@ export const tel = function ( formDataTree ) {
 		.map( val => val.trim() ).filter( val => '' !== val );
 
 	const isTelephoneNumber = text => {
+		text = text.replace( /[#*].*$/, '' ); // Remove extension
 		text = text.replaceAll( /[()/.*#\s-]+/g, '' );
 
-		return /^[+]?[0-9]+$/.test( text );
+		const international = text.startsWith( '+' ) || text.startsWith( '00' );
+
+		if ( international ) {
+			text = `+${ text.replace( /^[+0]+/, '' ) }`;
+		}
+
+		if ( ! /^[+]?[0-9]+$/.test( text ) ) {
+			return false;
+		}
+
+		if ( ! ( 6 < text.length && text.length < 16 ) ) {
+			return false;
+		}
+
+		return true;
 	};
 
 	if ( ! values.every( isTelephoneNumber ) ) {