From Wiktionary, the free dictionary
siết (“to tighten”) + chặt (“tight”).
siết chặt
- (literal) to tighten by gripping very hard
- (figurative) to tighten (enforcement, management, inspection, etc.)
- Antonym: nới lỏng (“to loosen”)
- siết chặt quản lí nhà nước ― to tighten or consolidate state managerial enforcement