This effectively separated Daun from Saltykov. Knowing, though, that Loudon's corps was not sufficient to fully support the Russian ally, he sent also Count András Hadik's 17,000-man observation corps from northern Bohemia. This corps had been shadowing Henry's army and Hadik broke off his contact with Henry's force on 22 July, crossing into Lusatia at Zwickau. Upon orders from Empress Elizabeth, Saltykov moved on Prussia in a methodical advance beginning in June 1759. Some estimates place his army as high as 70,000 men; others suggest he had approximately 41,000 in June and July. Upon learning of this advance, Frederick ordered General Dohna to halt the Russian westward advance. Dohna had a force of 26,000 at his disposal, including several companies of cavalry. In mid-July, Dohna and Saltykov spent a week feinting with each other as Saltykov drew closer to the Prussian border. On 14 July, he turned southwest, making for the Oder river, somewhere between Crossen and Glogau. By 19 July, he had reached the Silesian front near Züllichau (Sulechów), where Saltykov planned to rest his troops for a couple of days. The third commander of the Russian force in three years, he was still relatively new to the command of this army, and spent a couple of days consulting with his chief officers and getting to know the strengths and weaknesses of his army, and letting them get to know him. In a course of meetings with his staff, however, he excluded the Austrian commanders with him, a telling comment on his distrust of the Habsburg staff. Monitoring this from afar, and dissatisfied with Dohna's timidity in bringing Saltykov to battle, Frederick sent Carl Heinrich von Wedel to take command. Wedel arrived on 20 July and established a blocking position at Züllichau. This would prevent the Russians from entering Prussian territory and reaching the Oder. He wanted to attack the Russians at dawn the next day, but could not find an appropriately weak location in the Russian defenses. On the same day as Wedel arrived, 20 July, Saltykov established himself astride the Prussian communication line at the Oder, strengthening his already formidable position. This effectively cut any Prussian advance or reinforcement from Crossen (Krosno) or Frankfurt on the Oder.