Was there some law formed in US after Jonestown mass suicide, regarding religious or such kind of clique/sect/cabals? or what actions were taken regarding limiting and monitoring cult activities by US government?
What the current Wikipedia entry says on this is accurate and succinct:
In the United States religious activities of cults are protected under the First Amendment, however cult members are not granted any special protection against criminal charges.
In other words, no law is allowed in the USA that abridges anyone's right to join a religion of their choice, or to pick who they can or can't associate with. Laws are certainly allowed against poisoning children and murdering congressmen, but those laws already existed.
Of course even that amount of freedom from government oversight wasn't enough for Jim Jones and his cult, which is why they removed themselves from the jurisdiction of US law entirely by relocating to Guyana (in South America). No US law could reach them there.
The citation in the Wikipedia entry is an excellent paper on cult law in the US. There are no laws to "monitor" anybody to see when they go wrong; the standard law-enforcement and judicial procedures used to catch other wrong-doers apply to cults as well. Who decides what is a cult anyway? Freedom of expression is other peoples' freedom to say/preach things you find nasty. Otherwise that freedom means nothing.