KIEV, Ukraine (AP) — At least eight civilians have been killed by fighting and shelling in two Ukrainian cities held by separatist militants, officials in the rebellion-wracked east said Monday.

Authorities in Luhansk that five people were killed and 15 injured by overnight artillery strikes. Three were killed in Donetsk as a result of clashes, the city's government said.

Territory between the cities has seen intensified fighting as government troops try to gain control over the area where a Malaysia Airlines plane was downed earlier this month.

Dutch and Australian police set off for the crash site Monday morning in a convoy of 20 cars, aiming to secure the area so that investigations can continue and any remaining bodies can be recovered.

Both sides in the conflict have traded accusations over the mounting civilian death toll. The armed conflict that has been raging for more than three months has displaced more than 200,000 people.

Rebels accuse government troops of deploying artillery against residential areas. Authorities deny that charge, but also complain of insurgents using apartment blocks as firing positions.

The U.S. State Department on Sunday released satellite images that it says back up its claims that rockets have been fired from Russia into eastern Ukraine and heavy artillery for separatists has also crossed the border.

Russian Foreign Minister Sergey Lavrov dismissed the claims Monday during a televised press conference, asking "why it took ten days" before the U.S. released the images.

A four-page document released by the State Department appears to show blast marks from where rockets were launched and craters where they landed. Officials said the images, sourced from the U.S. Director of National Intelligence, show heavy weapons fired between July 21 and July 26 — after the July 17 downing of Malaysia Airlines Flight 17.

The images could not be independently verified by The Associated Press.

Lavrov said he is expecting OSCE observers to arrive at the Russian-Ukrainian border "in the coming days." He said they would see that accusations rebels are traveling freely into Ukraine from Russia are false.

Ukrainian officials have said the mission is largely pointless because it involves only about two dozen observers monitoring the 2,000 kilometer (1,240-mile) border between the two countries.

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Nataliya Vasilyeva in Moscow and Mstyslav Chernov in Donetsk contributed to this report.