There are some minor events related to reinforcement.

Nomonhan was a small village, located near the boundary between Empire of Manchukuo and the People's Republic of Mongolia. Both Manchukuo and Mongolia were protectorates of Japan and the Soviet Union, respectively.

The terrain surrounding Nomonhan was a low and undulating plain, somewhat marshy and interrupted by sand hills and the Halha River. It was a land of extreme climate; the summer temperature rose to 40 degrees while the winter temperature fell to -30 degrees Celsius.

This area was not suitable for large-scale habitation or intensive cultivation, and thus was very sparsely populated. A definite international border had not been delimited, and for centuries almost nobody cared. With the arrival of Japanese and Soviet forces to the area, however, de-facto borders had been established out of necessity. Naturally, these borders could not always be agreed upon...

The Japanese Kwantung Army (stationed in Manchukuo) claimed the Halha River as international boundary, while the Soviets and Mongolians claimed the border to be 15 miles to the east, near Nomonhan. A result of this indefinite border was the occasional small-scale incident between the Kwantung Army and its Manchuria allies, and the Soviets with their Mongolian allies....

In mid-May 1939, the Kwantung Army received a report that some 700 Mongolian horsemen had crossed the Halha River. The Kwantung Army dispatched the 23rd Division's reconnaissance regiment, under the Lt. Colonel Yaozo Azuma. the Azuma reconnaissance regiment quickly drove off the Mongolian horsemen. Azuma returned to Hailar in triumph.
The Soviets interrupted with an invasion then it dispatched a mechanized battalion and Mongolian cavalry in the area.

Hearing this, the Kwantung Army formed a task force, which consist of a battalion of 64th infantry regiment of 23rd Division, some Manchuria cavalries and the Azuma reconnaissance regiment, let by the Colonel Yamagata.

On the 28th of May, the Yamagata Task Force began its operations, which aimed to drive the Soviets and Mongolians away.

The Azuma reconnaissance regiment cut through the defensive perimeter and almost made it to vital bridges across the confluence of Halha and Holsten rivers. It was at this critical moment that Soviet Armor and infantry counterattacked, and Azuma's small force was completely encircled near Hill 733.

Meanwhile, Yamagata's main force had been bogged down by Soviet positions and could do nothing for the encircled Azuma force.

Despite having been cut off and completely lacking supply, Azuma's small force resisted bravely but its fate was sealed. At 1900 on the 29th of May, the Azuma reconnaissance regiment was totally destroyed. Lt. Colonel Azuma fell in battle.

After the annihilation of the Azuma force, Soviets and Mongolians left to the West Bank of Halha River. Yamagata also moved back, transporting the bodies of Azuma and his force.

This border clash became a of will for both the Kwantung Army and Soviets. Stalin appointed Georgi K. Zhukov to command of 57th Corps in Mongolia to halt the expected Japanese advance. The Kwantung Army wanted to avenge this small defeat, and prepared renewed offensive as the Soviets expected...

The soon-to-follow next battle would be far more bloody...

I used mainly Japanese materials. I recommend following book for American.

A. D. Coox, Nomonhan: Japan against Russia, 1939, Stanford, Stanford University Press, 1985.

Strategy and Tactics #158 "Red Sun/Red Star the Nomonhan Campaign, 1939"

John H. Ebert, III