On 14 January 1921, the commander of the British Forces in Iran, General Edmund "Tiny" Ironside, promoted Reza Khan, who had been leading the Tabriz battalion, to lead the entire brigade. About a month later, under British direction, Reza Khan led his 3,000-4,000 strong detachment of the Cossack Brigade, based in Niyarak, Qazvin, and Hamadan, to Tehran and seized the capital. He forced the dissolution of the previous government and demanded that Seyyed Zia'eddin Tabatabaee be appointed Prime Minister. Reza Khan's first role in the new government was as Commander of the Iranian Army, which he combined with the post of Minister of War. He took the title Sardar Sepah (), or Commander-in-Chief of the Army, by which he was known until he became Shah. While Reza Khan and his Cossack brigade secured Tehran, the Persian envoy in Moscow negotiated a treaty with the Bolsheviks for the removal of Soviet troops from Persia. Article IV of the Russo-Persian Treaty of Friendship allowed the Soviets to invade and occupy Persia, should they believe foreign troops were using it as a staging area for an invasion of Soviet territory. As Soviets interpreted the treaty, they could invade if events in Persia should prove threatening to Soviet national security. This treaty would cause enormous tension between the two nations until the Anglo-Soviet Invasion of Iran.