Belgrade's Studio B TV said he had been tracked down near Bosnia's Serbian border, and a senior state security official cited by Associated Press said he has been located but not arrested, and that authorities have been trying to persuade him to give himself up.
Separately, the Serb government denied that Mladic was in custody and had been taken to neighbouring Bosnia.
The one-time Bosnian Serb commander is one of the most wanted men in the former Yugoslavia, accused of leading ethnic cleansing in the Balkans.
Gen Mladic, 63, was indicted in 1995 for genocide for the 43-month siege of Sarajevo, which claimed 12,000 civilian lives, and for orchestrating the 1995 massacre of 8,000 unarmed Muslims at Srebrenica, the worst atrocity in Europe since World War II.
UN war crimes prosecutor Carla Del Ponte has also officially denied that top Mladic had been arrested as Serb media have reported.
"We officially deny that (Ratko) Mladic has been arrested," Ms Del Ponte's spokeswoman Florence Hartmann told AFP.
"To our knowledge there is not even an operation ongoing to find him," she added, saying it was "media hype".
"We continue to put pressure on the Serbian government to act in accordance with the international arrest warrants and arrest him," she said.
EU warning on Mladic
The storm of conflicting reports about his status has exposed Belgrade's extreme jitters, a week before a key European Union decision on whether to freeze talks on Serbia's membership prospects unless Belgrade hands over Gen Mladic.
But the Serbian government has emphatically denied the speculation over Mladic.
"The news about Ratko Mladic is not correct," government spokesman Srdjan Djuric said.
"It is a manipulation which damages the (Serbian) government," he said in a statement.
However Belgrade has recently indicated it might move to appease the West.
Vladeta Jankovic, the top adviser to Serbian Prime Minister Vojislav Kostunica, hinted late on Monday that the former Bosnian Serb general might give himself up.
"This problem will be solved in the same way as previous problems related to those indicted for war crimes," said Mr Jankovic, referring to the voluntary surrender of 15 suspects since Kostunica took office in March 2004.
Besides Mladic, the only remaining war crimes suspects from the wars that shattered former Yugoslavia in the mid-1990s are his wartime political leader, Radovan Karadzic, and four other Serbs.
Mladic has been on the run since the war, widely believed to be in hiding on Serbian soil with the help of the military. Belgrade authorities have persistently denied any knowledge of his whereabouts.
In recent weeks the government of Serbia-Montenegro, the only remaining union between former Yugoslavia's six republics, has made a series of admissions in an attempt to appease the UN tribunal.
Among the revelations were that Mladic received medical treatment for an undisclosed illness at a Belgrade hospital under three different names in the 1990s.
In February, Serbia-Montenegro Defence Minister Zoran Stankovic said Belgrade was investigating more than 50 former soldiers suspected of helping him to evade capture at various stages over the past decade.
About a month earlier, Mr Stankovic admitted Mladic's pension had been picked up by his son.
The retired general lived openly in Belgrade until the fall of Milosevic in 2000, and drew his pension via surrogates until last year, fuelling Western suspicion of Belgrade.