Block access to an ip and port using iptables on my routers

I have setup 2 routers as follows:

Router (A) connects to internet, Router (B) WAN port connects to the LAN port of the Router A making it a gateway behind another gateway.

Router A LAN/Gateway IP: 192.168.1.1

Router B WAN IP: 192.168.1.2 and Gateway IP after NAT: 192.168.2.1

I am trying to block access to the Router A’s admin page hosted on 192.168.1.1 from the LAN of Router B whose LAN IP addr are 192.168.2.1/24. I used the following on the firewall of Router B, which seems to be failing.

#iptables -I OUTPUT -d 192.168.1.1 -p tcp --dport 80 -j REJECT --reject-with tcp-reset

Can anyone tell me where I went wrong?

UPDATE:
This is the solution..

iptables -I FORWARD -d 192.168.1.1 -p tcp --dport 80 -j REJECT --reject-with tcp-reset

Thanks!
KK