Russian President Vladimir Putin and Belarusian President Alexander Lukashenko say they will boost cooperation in the military industry and other fields.
The leaders met in the second largest Russian city, St. Petersburg, on Sunday.
Putin said at the start of the talks that the two countries are developing ties in all areas, including economy, education and culture.
Lukashenko responded that the two sides are seriously discussing how to develop their economies and military industries.
Russia and Belarus are under sanctions by Western countries over the ongoing invasion of Ukraine.
Putin and Lukashenko will attend a meeting on Monday to reaffirm bilateral economic and security collaboration with the aim of establishing a union state.
Meanwhile, Ukraine's security service on Saturday announced an investigation into five people on suspicion of attempting to embezzle about 40 million dollars in the procurement of mortar rounds.
It said former and current high-ranking officials of Ukraine's defense ministry and heads of affiliated companies had been involved in the alleged scheme.
The agency said the ministry sealed a contract for 100,000 shells with an arms supplier in August 2022, with full payment made in advance. But it added that none of the munitions were delivered.
A series of corruption cases has come to light in Ukraine, putting the government under close public scrutiny.
Western countries, which have been supplying military aid to help Ukraine defend itself against the Russian invasion, are also urging Kyiv to redouble its efforts to root out graft.