Merkel is due to attend the talks in the capital of Belarus at 6.30 p.m. local time (15.30 GMT) as intense fighting continues in eastern Ukraine and Ukrainian President Petro Poroshenko declared earlier Wednesday that he was ready to introduce martial law throughout Ukraine if the conflict with pro-Russian separatists escalated any further.
Government spokesman Steffen Seibert told journalists at a press conference in Berlin: "The realization of this visit means a glimmer hope, but nothing more for the moment.
"As Chancellor Merkel publicly said in the past couple of days it is still uncertain whether these talks will be successful."
"But despite all the uncertainties, this initiative is in the interest of people who suffer in eastern Ukraine," Seibert said.
Martial law considered
He declined to comment on the details of the ongoing negotiations among diplomats of the four countries.
He also told a Cabinet meeting ahead of the Minsk negotiations: "The government and parliament are ready to introduce martial law throughout Ukraine ... I will not hesitate with this decision if the actions of the aggressor lead to further escalation."
Merkel and Russian President Vladimir Putin travelled to Kiev and Moscow last week to convince Poroshenko and Russian President Vladimir Putin that the violence in eastern Ukraine needed to be halted.
However, the European leaders failed to broker a cease-fire deal, but agreed to continue talks.
U.S. and European leaders accuse Russia of supporting the conflict with arms and ammunition, while Russia says the U.S. and EU have deliberately destabilized Ukraine to expand the west's military presence in Eastern Europe through NATO.
- 'Lethal aid'
More than 5,300 people have been killed and 12,200 others injured in eastern Ukraine since mid-April last year in the ongoing conflict, according to the U.N. High Commissioner for Human Rights.
The Ukrainian government and pro-Russian separatists signed a cease-fire agreement in the Belarusian capital of Minsk on Sept. 5, but both sides have violated it.
Fighting has increased in recent weeks as separatist fighters backed by Russia seek to expand their control in the east of the country.
The Ukrainian military claimed Monday that 1,500 Russian troops had crossed its border with convoys of military hardware, including Grad rocket systems.
The U.S. administration recently said it could provide Ukraine with lethal military aid, a move which received a lukewarm response from Washington's European allies.