DONETSK, Ukraine (AFP) - Ukraine's pro-Russian rebels defied mounting world outrage on Sunday and said they would allow international monitors to safely access the site of downed Malaysia Airlines Flight MH17 only if Kiev agreed to a truce.
The tough terms were set as global anger rose at an increasingly isolated Russia over its perceived failure to pressure the insurgents into opening passage to where the remains of 298 victims whose lives were cut short on Thursday lay scattered in stifling heat along wheat and sunflower fields.
Insurgents who have been in control of Ukraine's eastern rustbelt since early April had allowed only limited freedom of manoeuver to a 30-member team of monitors from the Organisation for Security and Cooperation in Europe (OSCE) who have been trying to assure respectful treatment of the remains since Friday.
Ukraine accuses Russia of helping the gun-toting militias of hiding and destroying vital evidence that could prove their alleged involvement in the downing of the Malaysia Airline Boeing 777 on Thursday afternoon.
But top Russian officials and Moscow's state media have suggested that the new Kiev leaders staged the attack to blame the rebels and convince their Western allies to deploy troops and help seal Ukraine's porous border with its giant eastern neighbour.
US Secretary of State John Kerry told Russian counterpart Sergei Lavrov that Washington was "deeply concerned" that investigators were being denied "proper access" to the wreckage of MH17 that was flying from Amsterdam to Kuala Lumpur when it crashed.
And Dutch Prime Minister Mark Rutte - his shocked nation flying flags at half mast over the weekend in mourning over 192 lost compatriots - said he had urged Russian President Vladimir Putin during a "very intense" call to "take responsibility" for a credible probe.
Investigators from the Netherlands were set to arrive in eastern Ukraine on Sunday.
Moscow released a terse statement after Kerry's talks with Lavrov calling for "material evidence, including black boxes" to be handed over to international inspectors so that they could take immediate charge of an independent probe.
But Putin firmly denies exerting any control over the uprising and a top rebel commander sent an email to the media on Sunday putting conditions on unfettered access to the grisly site that Kiev has rejected for weeks.
"We declare that we will guarantee the safety of international experts on the scene as soon as Kiev concludes a ceasefire agreement," the self-proclaimed Donetsk People's Republic's deputy premier Andrei Purgin wrote.
- 'Like 9/11 and Lockerbie' -
The rebel added in explosive language that has characterised the public relations battle being waged amid the crisis that Kiev's failure to strike a deal would give the impression that the government was made up of "dangerous lunatics (and) bloodthirsty maniacs".
Ukrainian President Petro Poroshenko - a 48-year-old chocolate baron who won a May election following the ouster of a Kremlin-backed regime - ripped up a shaky truce on July 1 and has refused to announce a new one until the separatists give up their arms.
Poroshenko spent much of the day Saturday pressing world leaders to recognise the militias as a terrorist organisation that should be put on trial at the International Criminal Court in The Hague.
He told French President Francois Hollande that the downing near Ukraine's Russian border of flight MH17 was similar to such atrocities as the 2001 attacks on the United States.
"We see no difference between the events in Ukraine and what happened on September 11 in the United States or the tragedy over Scotland's Lockerbie," Poroshenko said in reference to the 1988 bombing for Pan Am Flight 103 that claimed nearly 300 lives.
The MH17 disaster came less than a day after the United States unleashed punishing sanctions against some of Russia's most important energy and military firms - most of them with links to Putin - and urged more hesitant European leaders to follow suit.
The European Union - many of its member states dependent on Russian gas - took the far less punitive step on Friday of curbing some future investments in Russia and leaving the option open for broader sanctions.
But British Prime Minister David Cameron raised the prospect on Saturday of fresh EU sanctions against Russia over the Malaysian plane crash, saying the West must "fundamentally change our approach" unless Moscow alters course in Ukraine.
"Russia can use this moment to find a path out of this festering, dangerous crisis. I hope it will do so. But if that does not happen then we must respond robustly," he wrote in an article in the Sunday Times.
Cameron added that confirmation of the plane being blown out of the sky at 33,000 feet (10,000) metres by a surface-to-air missile fired from an area held by the rebels would place the responsibility firmly on Russia.
"If it is the case, then we must be clear what it means: this is a direct result of Russia destabilising a sovereign state, violating its territorial integrity, backing thuggish militias, and training and arming them," Cameron wrote.
- Russia blasts Kiev 'radicals' -
The Kremlin has accused Western leaders of assigning responsibility before any firm conclusions from an independent probe were reached.
Russia's Deputy Defence Minister Anatoly Antonov went on state television on Saturday to demand answers to 10 "simple" questions from the Ukrainian government that would help determine the true culprit.
"Answers to these questions would allow all of us... to try and find an answer to the most important question: what happened in the sky over Ukraine," Antonov said.
The pro-Kremlin speaker of Russia's lower house of parliament also told state television that Kiev was "continuing to violate basic norms of international law and fundamental human rights".
"And this, without doubt, prompts radical lawmakers and aggressive nationalists to take corresponding steps," State Duma speaker Sergei Naryshkin said.