In the far north, Finland had taken this opportunity to recover territory lost during the Winter War. On 26th June Finland declared war on the USSR (although apparently Soviet aircraft attacked Finnish cities and airfields the day before). The Finns (under Mannerheim) launched their main attacks on 10th July. The Karelia Army north of Lake Ladoga attacked towards Petrozavodsk and Olonets against the Soviet 7th Army, while the Karelia Army on the Karelian Isthmus applied pressure against the Soviet 23rd Army defending the fortified positions immediately north of Leningrad. On 16th July the Finnish 7th Corps reached Sortavala on the north shore of Lake Ladoga (effectively separating the 7th and 23rd Armies) and continued to advance south-east to reach Salmi on 21st July. By 26th July the Finns had reached Petrozavodsk on the west shore of Lake Onega, but by now the Soviet resistance had stiffened and they continued fighting to the west of the Finns’ advance line, including as far east as Sortavala. The Soviet 7th Army continued to put up dogged resistance so that by early August the Finns were only about halfway to their objective, which was the Svir River line.