Pro-Russia rebels fired missiles Friday at government troops near the Russian border, killing at least 19 servicemen, Ukraine's Defense Ministry said, adding that four other troops died elsewhere in eastern Ukraine.

The statement revised an earlier ministry report of 30 troops killed in the pre-dawn attack at a forward operating base in eastern Ukraine.

Defense Ministry spokesman Vladislav Seleznev gave the figure of 19 on his Facebook account and reported the four other troop deaths. He did not elaborate on those circumstances.

Ukrainian government troops have been fighting for more than three months against separatists in eastern Ukraine. In the last two weeks, however, they have cut the territory held by the rebels in half and forced them out of their stronghold in the city of Slovyansk. The rebels have since regrouped in Donetsk, an eastern industrial city of 1 million, and Ukraine has vowed to cordon the area.

The Defense Ministry said the troops struck in Friday's attack had been trying to secure the porous border with Russia, which Ukraine says has been crossed by large numbers of militants transporting armored vehicles and weapons. It said 93 soldiers were injured in the clash.

Rockets were fired from a Grad missile launcher around 15 kilometers (nearly 10 miles) away, the ministry said.

The operating base was located near one of three border crossings whose closure Russian officials had announced Friday.

Border crossings are of particular concern to both sides. Ukraine says Russia is supporting and arming the rebels, but Russia denies the charges. The rebels have captured a few of the border crossings and Ukraine has demanded them back.

Russian news agencies quoted Vasily Malayev, spokesman for the Federal Security Service in the Rostov region, as saying the border crossings east of Donetsk were temporarily closed late Thursday because of fighting.

Ukraine on Friday said it had regained control of one of those rebel-held crossings.