South Korea's top two telecoms operators SK Telecom and KT Corp said on Tuesday they had suspended online sale of Apple's popular iPad 2 tablet due to tight supplies less than a week after they launched the sale.

Our iPad 2 inventory has been depleted and we apologize for failing to provide enough supplies due to the product's global supply shortages, SK Telecom said in a posting on its website.

The companies declined to reveal sales.

Apple sold just under 5 million iPads in the March quarter versus estimates of up to 6 million, as the transition to a new model and Japanese supply chain tangles triggered shortages of critical components.

Apple launched the new version of iPad in Japan, Hong Kong, Korea, Singapore and eight additional countries last week after it went on sale in the U.S. market in March.

Korean telecom operators are betting heavily on tablet and smartphone sales to make up for weak growth in voice traffic revenue.

SK Telecom on Tuesday also announced record investment plan of 2.3 trillion won ($2.2 billion) to handle the data explosion stemming from the surging popularity of smartphones.

(Reporting by Hyunjoo Jin and Miyoung Kim)