Undated (AP) _ Here is a chronology of U.S.-Iranian encounters in the Persian Gulf since May of last year, when the Pentagon announced increased U.S. presence in the waterway to protect Kuwaiti ships.

May 29 - Pentagon officials report a major U.S. military buildup in the gulf is planned to protect Kuwaiti tankers.

July 18-20 - United States begins reflagging of 11 Kuwaiti tankers with U.S. flag.

July 21 - U.S. begins convoy operations, escorting Kuwaiti ships.

Aug. 8 - U.S. Navy F-14 Tomcat fighter fires two missiles at Iranian jet approaching an unarmed U.S. surveillance plane. Both missiles miss but Iranian jet retreats.

Aug. 20 - Iran admits sowing mines to ''defend our coastline.''

Sept. 21 - U.S. helicopter attacks Iranian ship found to be laying mines. Iranian ship left ''dead in the water'' after fire on board is extinguished.

Oct. 8 - U.S. helicopter gunships sink three Iranian patrol boats after an American observation helicopter is fired on. Two of six Iranian crewmen picked out of gulf waters later die.

Oct. 16 - Iranian missile hits Kuwaiti ship flying the U.S. flag, blinding its American captain and wounding 17 other crewmen in the first direct attack on the tanker fleet guarded by the United States.

Oct. 19 - U.S. warships destroy two Iranian oil platforms in the Persian Gulf in retaliation.

Nov. 2 - The frigate USS Carr, on escort duty, fires machine guns to chase off three small vessels, thought to be Iranian. At least one of the vessels later turns out to be a private fishing boat, and one Indian crew member was killed.

Nov. 6 - Iranian commandos shoot up a U.S.-managed tanker from a speedboat, but no casualties are reported.

Nov. 16 - Iranian speedboats attack a U.S.-owned supertanker and three other ships in the southern gulf.

Dec. 12 - A Navy warship and television helicopter rescue 40 people from a burning supertanker, which had been attacked by an Iranian gunboat.

March 6 - U.S. helicopters draw heavy machine gun fire from an oil platform and small boats in the central gulf, but do not return fire.

April 14 - The USS Samuel B. Roberts strikes a mine, seriously damaging the frigate. Ten American sailors are injured.

April 18 - American forces attack two Iranian oil platforms in retaliation for mining the Roberts, triggering daylong fighting in which Iran loses six naval craft including two of its best frigates. One U.S. helicopter is missing after the clash.

April 22 - Pentagon officials say U.S. warships will be allowed to intervene in attacks on non-U.S. vessels.

April 29 - U.S. formalizes new policy of interceding in Iranian attacks on ''friendly, innocent neutral'' vessels in international waters. U.S. announces 2 Marine helicopter crewmen lost April 18 are listed as killed in action but does not say helicopter was shot down.

May 16 - U.S. finds Cobra helicopter wreckage, recovers pilots' bodies.

July 2 - Frigate Elmer Montgomery intervenes in Iranian gunboat attack on Danish tanker, first time under new rules of engagement allowing protection of non-U.S. flag ships.

July 3 - Vincennes accidentally shoots down Iranian jetliner with 290 killed during clash with Iranian gunboats in the Strait of Hormuz. Plane mistaken for F-14, U.S. says.