Opposition demonstrators have delivered an ultimatum for a new leader to be appointed by tomorrow or they will step up efforts to topple a government clinging to power after premier Yingluck Shinawatra was ousted by the courts.
"Forming an unelected government is illegitimate and will bring more conflict and violence," warned Tarit Pengdith, head of the Ministry of Justice's Department of Special Investigation (DSI).
Officials will "step up law enforcement to solve the problems", said Tarit during a televised briefing by the government agency in charge of the security response to the six-month political stand-off.
Fanning tensions, two people were wounded in an explosion, thought to be caused by a grenade, near the government headquarters late yesterday, officials said.
Yingluck's removal -- for abusing her power with the controversial transfer of a senior security official has been denounced by her supporters as part of a "judicial coup".
The kingdom's long-running crisis broadly pits the Shinawatra family and its supporters -- mostly from northern Thailand -- against a royalist establishment with backing in Bangkok and the south.
The opposition says that the remaining caretaker government is no longer legitimate and that elections in the current climate will not solve the stalemate.
It wants an interim premier to be appointed to oversee vague reforms to tackle corruption before new elections are held in about 18 months' time.
The pro-government "Red Shirts", who kicked off a major rally this weekend on the outskirts of Bangkok, have warned that a power grab could lead to civil war.
"We will only stop our protest when justice is served," Red Shirts leader Jatuporn Prompan said today.
While the two groups of rival protesters have set up their camps in different parts of the capital, officials are on alert for possible clashes between the two sides.
Worsening violence could increase the chances of the coup-prone army intervening again.