Roche on Monday extended its $5.7 billion (3.5 billion pound) hostile offer for Illumina until March 23, a move that was widely expected as the Swiss drugmaker is keen to boost its position in the gene sequencing market.

All other terms and conditions of the offer remain unchanged, Basel-based Roche said in a statement.

Illumina has already adopted a poison pill defence strategy for Roche's unsolicited of $44.50 per share bid. It told shareholders not to tender any of their shares to Roche, saying the offer failed to properly value its existing and coming products.

The San Diego-based firm makes machines that decode a person's entire genome, going far beyond simple genetic tests that are already used in diseases such as cancer to test for a handful of gene variations.

A deal would give Roche's diagnostics unit a leading position in the market for gene sequencing, which can help better identify which patients benefit from a given drug.

Analysts say Roche, which has a history of success with such hostile takeouts, may have to raise its bid to around $60 per share to win Illumina.

Earlier acquisitions, such as that of diagnostic test-maker Ventana or U.S. biotech group Genentech, show Roche is happy to take its time with deals and that it will ultimately prevail with a sweetened offer.

Roche took seven months to buy Ventana for $3.4 billion in 2008, when Chief Executive Severin Schwan was head of its diagnostics unit. It first made an unsolicited, low-end bid before increasing its original offer by 19 percent.

Roche's offer for Illumina was due to expire on February 24.

(Reporting by Catherine Bosley. Editing by Jane Merriman)