9–13 April: KLA offensive

On 9 April 1999, at 03:00, an artillery barrage began from the Albanian side of the border, aimed in the direction of the Košare military outpost, which was occupied by the Yugoslav Army, in what became one of the bloodiest battles of the Kosovo War.^[23] The Albanians attacked in three directions, the first was towards Rrasa e Koshares, the second was towards the well-defended Košare outpost and the third was towards Maja Glava. Approximately 136 KLA soldiers^[8] reached the border and attacked Yugoslav positions. At that time less than 200 members of the Yugoslav Army were stationed at the front line. Bloody fighting ensued and lasted the whole day with 4 dead and one wounded on the Albanian side and 23 dead on the Yugoslav side.^[24] Later, the KLA seized the peak of Rrasa e Koshares and immediately began entrenching themselves. Serbian reports claimed that the KLA insurgents were assisted by British, French, German and Italian special forces.^[25]

The battle continued until the next morning. Then, with artillery support, the KLA took Maja Glava and continued to bombard the Košare Outpost, which resulted in the Yugoslav soldiers having to abandon their posts.^[26] At 19:00, members of the KLA entered the abandoned outpost and CNN and the British BBC broadcast images of a great number of KLA militants taking the outpost.^{[citation needed]}

Members of the Yugoslav Forces then retreated towards the second line of defense above the outpost. Those positions were easier to defend. The next day, Yugoslav reserve troops arrived to relieve the First Army. One batch of KLA soldiers managed to cut the Yugoslav line of communications, and managed to disable one BOV armoured personnel carrier. During the night, the KLA attacked the Yugoslav Army at Opijaz, trying to shatter the resistance of the Yugoslav soldiers, but all of the attacks were unsuccessful and resulted in the Yugoslav Army inflicting heavy losses on the KLA insurgents. Meanwhile, the Yugoslavs managed to bring in their Special Forces and also a few artillery pieces.^{[citation needed]}

On 13 April, the Yugoslav and Albanian armies clashed at the border near Krumë.^[27][28]

14 April: Yugoslav counter-offensive on Maja Glava

Albanian Army and KLA artillery continued to shell the Yugoslav Army's positions from Maja Glava and Rrasa e Koshares. The Yugoslav Army Headquarters decided to launch a sudden attack and surprise the enemy. On 14 April, Yugoslav troops attacked Maja Glava. The distance between the two enemy trenches wasn't longer than 50 meters. The Yugoslav Army was unable to take Maja Glava completely, but it prevented the Albanians' artillery from engaging them from their positions. The Maja Glava front was stabilized until the end of the war, without any changes on the lines.^{[citation needed]}

In April, there weren't any changes on the front lines at Rrasa e Koshares and both sides suffered heavy losses.

10–11 May: Yugoslav offensive on Rrasa e Koshares

May began with several unsuccessful attacks by the Yugoslav Army to take back the Košare outpost. The attacks were made unsuccessful because of the constant artillery fire aimed at their positions. On 6 May, the Yugoslav Army counterattacked at Rrasa e Koshares, in an effort to halt the artillery bombardment. A bloody skirmish ensued, but the Yugoslav Army did not manage to take Rrasa e Koshares. On 10 May, the Yugoslav Army sent two T-55 tanks to help stabilize the offensive on Rrasa e Koshares. When the tanks penetrated the KLA's lines, they advanced over 100 meters into insurgent-held territory, but the KLA still managed to retain control of Rrasa e Koshares. During the night of 10/11 May, NATO bombers dropped dozens of bombs on the Yugoslav troops who had attacked KLA positions around Rrasa e Koshares. At least in two of these instances NATO dropped cluster bombs on Yugoslav army troops. In these attacks, NATO killed eight Yugoslav soldiers and one officer and managed to wound over 40. The KLA seized the opportunity to attack and fought the Yugoslav soldiers out of their positions and forced them back.^{[citation needed]}

19–20 May: KLA attack near Junik

On 19 or 20 May, the KLA attacked a Yugoslav Special Forces' position near Junik. The KLA claimed to have managed to kill 14 Yugoslav Special Forces members after bitter fighting, whilst they suffered no losses. One of the killed was Russian citizen Bulakh Vitaly Glebovich. Documents retrieved from Glebovich's body showed he was an officer within the Russian Army, while Moscow confirmed that there was an officer by the same name who had been discharged from the Russian Army due to medical conditions with the name that the KLA had provided. The KLA presented this as evidence of Russian involvement in the war and sent a strong letter of protest to the Russian embassy in Tirana, demanding 5,000 firearms with ammunition as ransom for the retrieval of the body.^[29][30] Yugoslavia reported Glebovich was killed while fighting as a volunteer.^[18][31]

22 May: NATO friendly fire on Košare Outpost

On 22 May, NATO aircraft mistakenly bombed KLA positions.^[14] Some KLA commanders would later say that this was intentional to stop the KLA from making further gains.^[32] According to the KLA, seven of their fighters were killed and 27 wounded in the strike.^[14] After the war, PBS said that 67 people were reported as having died in the raid.^[13]